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 $51.92   3.141%   $53.5508   $53.55   $53.55   $53.60  
  Purchase #2 $88.46   9.199%   $96.5974   $96.60   $96.60   $96.60  
  Purchase #3 $216.71   4.834%   $227.1858   $227.19   $227.20   $227.20  
  Purchase #4 $130.96   11.327%   $145.7938   $145.79   $145.80   $145.80  
  Purchase #5 $78.54   7.693%   $84.5821   $84.58   $84.60   $84.60  
  Purchase #6 $117.54   6.824%   $125.5609   $125.56   $125.55   $125.60  
  Purchase #7 $27.81   3.648%   $28.8245   $28.82   $28.80   $28.80  
  7 purchase totals = $711.94       $762.0953   $762.09   $762.10   $762.20