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 $56.50   6.523%   $60.1855   $60.19   $60.20   $60.20  
  Purchase #2 $22.82   11.825%   $25.5185   $25.52   $25.50   $25.50  
  Purchase #3 $101.62   6.561%   $108.2873   $108.29   $108.30   $108.30  
  Purchase #4 $163.31   8.635%   $177.4118   $177.41   $177.40   $177.40  
  Purchase #5 $103.71   7.795%   $111.7942   $111.79   $111.80   $111.80  
  Purchase #6 $223.39   6.145%   $237.1173   $237.12   $237.10   $237.10  
  Purchase #7 $35.46   13.871%   $40.3787   $40.38   $40.40   $40.40  
  7 purchase totals = $706.81       $760.6933   $760.70   $760.70   $760.70