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 $65.86   13.510%   $74.7577   $74.76   $74.75   $74.80  
  Purchase #2 $237.91   9.649%   $260.8659   $260.87   $260.85   $260.90  
  Purchase #3 $80.91   7.460%   $86.9459   $86.95   $86.95   $86.90  
  Purchase #4 $55.91   8.484%   $60.6534   $60.65   $60.65   $60.70  
  Purchase #5 $157.97   11.871%   $176.7226   $176.72   $176.70   $176.70  
  Purchase #6 $199.62   3.693%   $206.992   $206.99   $207.00   $207.00  
  Purchase #7 $58.64   5.837%   $62.0628   $62.06   $62.05   $62.10  
  7 purchase totals = $856.82       $929.0003   $929.00   $928.95   $929.10