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 $64.34   5.812%   $68.0794   $68.08   $68.10   $68.10  
  Purchase #2 $242.69   6.864%   $259.3482   $259.35   $259.35   $259.30  
  Purchase #3 $115.81   3.528%   $119.8958   $119.90   $119.90   $119.90  
  Purchase #4 $56.61   9.338%   $61.8962   $61.90   $61.90   $61.90  
  Purchase #5 $145.78   11.578%   $162.6584   $162.66   $162.65   $162.70  
  Purchase #6 $213.98   10.767%   $237.0192   $237.02   $237.00   $237.00  
  Purchase #7 $11.52   5.476%   $12.1508   $12.15   $12.15   $12.20  
  7 purchase totals = $850.73       $921.0480   $921.06   $921.05   $921.10