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 $183.98   9.656%   $201.7451   $201.75   $201.75   $201.70  
  Purchase #2 $133.40   12.180%   $149.6481   $149.65   $149.65   $149.60  
  Purchase #3 $241.56   9.680%   $264.943   $264.94   $264.95   $264.90  
  Purchase #4 $37.93   8.542%   $41.17   $41.17   $41.15   $41.20  
  Purchase #5 $101.90   6.127%   $108.1434   $108.14   $108.15   $108.10  
  Purchase #6 $88.38   5.574%   $93.3063   $93.31   $93.30   $93.30  
  Purchase #7 $209.45   7.284%   $224.7063   $224.71   $224.70   $224.70  
  7 purchase totals = $996.60       $1,083.6622   $1,083.67   $1,083.65   $1,083.50