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 $212.92   6.739%   $227.2687   $227.27   $227.25   $227.30  
  Purchase #2 $143.49   13.793%   $163.2816   $163.28   $163.30   $163.30  
  Purchase #3 $83.75   5.345%   $88.2264   $88.23   $88.25   $88.20  
  Purchase #4 $141.55   7.131%   $151.6439   $151.64   $151.65   $151.60  
  Purchase #5 $158.60   12.148%   $177.8667   $177.87   $177.85   $177.90  
  Purchase #6 $235.85   11.821%   $263.7298   $263.73   $263.75   $263.70  
  Purchase #7 $167.66   4.131%   $174.586   $174.59   $174.60   $174.60  
  7 purchase totals = $1,143.82       $1,246.6031   $1,246.61   $1,246.65   $1,246.60