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 $175.73   11.269%   $195.533   $195.53   $195.55   $195.50  
  Purchase #2 $140.85   5.546%   $148.6615   $148.66   $148.65   $148.70  
  Purchase #3 $89.62   9.246%   $97.9063   $97.91   $97.90   $97.90  
  Purchase #4 $99.73   9.152%   $108.8573   $108.86   $108.85   $108.90  
  Purchase #5 $22.65   9.516%   $24.8054   $24.81   $24.80   $24.80  
  Purchase #6 $201.92   11.262%   $224.6602   $224.66   $224.65   $224.70  
  Purchase #7 $28.29   4.243%   $29.4903   $29.49   $29.50   $29.50  
  7 purchase totals = $758.79       $829.9140   $829.92   $829.90   $830.00