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 $48.68   3.221%   $50.248   $50.25   $50.25   $50.20  
  Purchase #2 $58.85   6.677%   $62.7794   $62.78   $62.80   $62.80  
  Purchase #3 $237.87   7.611%   $255.9743   $255.97   $255.95   $256.00  
  Purchase #4 $212.92   13.228%   $241.0851   $241.09   $241.10   $241.10  
  Purchase #5 $185.55   9.488%   $203.155   $203.16   $203.15   $203.20  
  Purchase #6 $144.39   3.366%   $149.2502   $149.25   $149.25   $149.30  
  Purchase #7 $10.27   13.660%   $11.6729   $11.67   $11.65   $11.70  
  7 purchase totals = $898.53       $974.1649   $974.17   $974.15   $974.30