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 $71.77   4.244%   $74.8159   $74.82   $74.80   $74.80  
  Purchase #2 $108.76   8.382%   $117.8763   $117.88   $117.90   $117.90  
  Purchase #3 $160.37   5.146%   $168.6226   $168.62   $168.60   $168.60  
  Purchase #4 $192.52   4.721%   $201.6089   $201.61   $201.60   $201.60  
  Purchase #5 $182.64   10.119%   $201.1213   $201.12   $201.10   $201.10  
  Purchase #6 $239.32   8.781%   $260.3347   $260.33   $260.35   $260.30  
  Purchase #7 $20.89   8.179%   $22.5986   $22.60   $22.60   $22.60  
  7 purchase totals = $976.27       $1,046.9783   $1,046.98   $1,046.95   $1,046.90