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 $58.63   8.367%   $63.5356   $63.54   $63.55   $63.50  
  Purchase #2 $99.85   5.484%   $105.3258   $105.33   $105.35   $105.30  
  Purchase #3 $198.63   7.179%   $212.8896   $212.89   $212.90   $212.90  
  Purchase #4 $75.71   6.862%   $80.9052   $80.91   $80.90   $80.90  
  Purchase #5 $126.68   4.631%   $132.5466   $132.55   $132.55   $132.50  
  Purchase #6 $89.96   3.496%   $93.105   $93.11   $93.10   $93.10  
  Purchase #7 $194.70   5.336%   $205.0892   $205.09   $205.10   $205.10  
  7 purchase totals = $844.16       $893.3970   $893.42   $893.45   $893.30