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 $58.76   9.805%   $64.5214   $64.52   $64.50   $64.50  
  Purchase #2 $177.46   9.294%   $193.9531   $193.95   $193.95   $194.00  
  Purchase #3 $128.45   11.353%   $143.0329   $143.03   $143.05   $143.00  
  Purchase #4 $65.86   6.825%   $70.3549   $70.35   $70.35   $70.40  
  Purchase #5 $230.56   9.194%   $251.7577   $251.76   $251.75   $251.80  
  Purchase #6 $70.32   4.565%   $73.5301   $73.53   $73.55   $73.50  
  Purchase #7 $62.76   10.463%   $69.3266   $69.33   $69.35   $69.30  
  7 purchase totals = $794.17       $866.4767   $866.47   $866.50   $866.50