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 $194.33   5.252%   $204.5362   $204.54   $204.55   $204.50  
  Purchase #2 $229.33   3.409%   $237.1479   $237.15   $237.15   $237.10  
  Purchase #3 $139.51   8.643%   $151.5678   $151.57   $151.55   $151.60  
  Purchase #4 $168.45   8.818%   $183.3039   $183.30   $183.30   $183.30  
  Purchase #5 $182.82   10.734%   $202.4439   $202.44   $202.45   $202.40  
  Purchase #6 $230.26   8.654%   $250.1867   $250.19   $250.20   $250.20  
  Purchase #7 $230.48   9.573%   $252.5439   $252.54   $252.55   $252.50  
  7 purchase totals = $1,375.18       $1,481.7303   $1,481.73   $1,481.75   $1,481.60