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 $29.54   8.874%   $32.1614   $32.16   $32.15   $32.20  
  Purchase #2 $159.26   5.671%   $168.2916   $168.29   $168.30   $168.30  
  Purchase #3 $52.79   7.201%   $56.5914   $56.59   $56.60   $56.60  
  Purchase #4 $31.43   4.216%   $32.7551   $32.76   $32.75   $32.80  
  Purchase #5 $59.94   6.366%   $63.7558   $63.76   $63.75   $63.80  
  Purchase #6 $12.49   7.652%   $13.4457   $13.45   $13.45   $13.40  
  Purchase #7 $213.40   10.382%   $235.5552   $235.56   $235.55   $235.60  
  7 purchase totals = $558.85       $602.5562   $602.57   $602.55   $602.70