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 $92.70   12.139%   $103.9529   $103.95   $103.95   $104.00  
  Purchase #2 $5.57   13.690%   $6.3325   $6.33   $6.35   $6.30  
  Purchase #3 $76.80   13.668%   $87.297   $87.30   $87.30   $87.30  
  Purchase #4 $175.79   6.655%   $187.4888   $187.49   $187.50   $187.50  
  Purchase #5 $26.42   13.137%   $29.8908   $29.89   $29.90   $29.90  
  Purchase #6 $227.40   7.474%   $244.3959   $244.40   $244.40   $244.40  
  Purchase #7 $126.71   7.300%   $135.9598   $135.96   $135.95   $136.00  
  7 purchase totals = $731.39       $795.3177   $795.32   $795.35   $795.40