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 $30.28   10.428%   $33.4376   $33.44   $33.45   $33.40  
  Purchase #2 $32.30   11.792%   $36.1088   $36.11   $36.10   $36.10  
  Purchase #3 $202.60   3.531%   $209.7538   $209.75   $209.75   $209.80  
  Purchase #4 $126.76   5.261%   $133.4288   $133.43   $133.45   $133.40  
  Purchase #5 $26.59   11.773%   $29.7204   $29.72   $29.70   $29.70  
  Purchase #6 $56.98   6.121%   $60.4677   $60.47   $60.45   $60.50  
  Purchase #7 $229.85   6.499%   $244.788   $244.79   $244.80   $244.80  
  7 purchase totals = $705.36       $747.7051   $747.71   $747.70   $747.70