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 $98.95   5.689%   $104.5793   $104.58   $104.60   $104.60  
  Purchase #2 $126.33   4.561%   $132.0919   $132.09   $132.10   $132.10  
  Purchase #3 $47.40   5.266%   $49.8961   $49.90   $49.90   $49.90  
  Purchase #4 $134.98   8.777%   $146.8272   $146.83   $146.85   $146.80  
  Purchase #5 $190.86   10.661%   $211.2076   $211.21   $211.20   $211.20  
  Purchase #6 $92.74   12.607%   $104.4317   $104.43   $104.45   $104.40  
  Purchase #7 $64.92   7.847%   $70.0143   $70.01   $70.00   $70.00  
  7 purchase totals = $756.18       $819.0481   $819.05   $819.10   $819.00