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 $91.95   3.302%   $94.9862   $94.99   $95.00   $95.00  
  Purchase #2 $112.51   8.304%   $121.8528   $121.85   $121.85   $121.90  
  Purchase #3 $34.78   13.641%   $39.5243   $39.52   $39.50   $39.50  
  Purchase #4 $238.84   7.810%   $257.4934   $257.49   $257.50   $257.50  
  Purchase #5 $97.87   3.706%   $101.4971   $101.50   $101.50   $101.50  
  Purchase #6 $147.70   4.584%   $154.4706   $154.47   $154.45   $154.50  
  Purchase #7 $61.93   11.286%   $68.9194   $68.92   $68.90   $68.90  
  7 purchase totals = $785.58       $838.7438   $838.74   $838.70   $838.80