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 $39.51   4.384%   $41.2421   $41.24   $41.25   $41.20  
  Purchase #2 $158.69   11.606%   $177.1076   $177.11   $177.10   $177.10  
  Purchase #3 $154.66   12.231%   $173.5765   $173.58   $173.60   $173.60  
  Purchase #4 $57.48   12.655%   $64.7541   $64.75   $64.75   $64.80  
  Purchase #5 $88.46   8.376%   $95.8694   $95.87   $95.85   $95.90  
  Purchase #6 $225.98   12.297%   $253.7688   $253.77   $253.75   $253.80  
  Purchase #7 $207.26   4.115%   $215.7887   $215.79   $215.80   $215.80  
  7 purchase totals = $932.04       $1,022.1072   $1,022.11   $1,022.10   $1,022.20