Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $132.66   13.852%   $151.0361   $151.04   $151.05   $151.00  
  Purchase #2 $184.92   12.799%   $208.5879   $208.59   $208.60   $208.60  
  Purchase #3 $110.28   7.283%   $118.3117   $118.31   $118.30   $118.30  
  Purchase #4 $207.36   11.628%   $231.4718   $231.47   $231.45   $231.50  
  Purchase #5 $118.50   7.422%   $127.2951   $127.30   $127.30   $127.30  
  Purchase #6 $139.44   10.232%   $153.7075   $153.71   $153.70   $153.70  
  Purchase #7 $245.67   10.796%   $272.1925   $272.19   $272.20   $272.20  
  7 purchase totals = $1,138.83       $1,262.6026   $1,262.61   $1,262.60   $1,262.60