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 $67.94   11.322%   $75.6322   $75.63   $75.65   $75.60  
  Purchase #2 $232.54   12.574%   $261.7796   $261.78   $261.80   $261.80  
  Purchase #3 $96.64   12.280%   $108.5074   $108.51   $108.50   $108.50  
  Purchase #4 $149.42   13.815%   $170.0624   $170.06   $170.05   $170.10  
  Purchase #5 $56.63   8.651%   $61.5291   $61.53   $61.55   $61.50  
  Purchase #6 $143.99   7.712%   $155.0945   $155.09   $155.10   $155.10  
  Purchase #7 $22.34   5.244%   $23.5115   $23.51   $23.50   $23.50  
  7 purchase totals = $769.50       $856.1167   $856.11   $856.15   $856.10