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 $44.44   9.274%   $48.5614   $48.56   $48.55   $48.60  
  Purchase #2 $194.56   6.346%   $206.9068   $206.91   $206.90   $206.90  
  Purchase #3 $155.68   6.591%   $165.9409   $165.94   $165.95   $165.90  
  Purchase #4 $40.51   12.183%   $45.4453   $45.45   $45.45   $45.40  
  Purchase #5 $60.35   12.638%   $67.977   $67.98   $68.00   $68.00  
  Purchase #6 $86.90   8.777%   $94.5272   $94.53   $94.55   $94.50  
  Purchase #7 $161.86   3.816%   $168.0366   $168.04   $168.05   $168.00  
  7 purchase totals = $744.30       $797.3952   $797.41   $797.45   $797.30