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 $192.84   3.667%   $199.9114   $199.91   $199.90   $199.90  
  Purchase #2 $113.80   10.854%   $126.1519   $126.15   $126.15   $126.20  
  Purchase #3 $98.71   11.415%   $109.9777   $109.98   $110.00   $110.00  
  Purchase #4 $46.77   4.209%   $48.7385   $48.74   $48.75   $48.70  
  Purchase #5 $118.70   6.426%   $126.3277   $126.33   $126.35   $126.30  
  Purchase #6 $223.51   5.664%   $236.1696   $236.17   $236.15   $236.20  
  Purchase #7 $6.79   8.738%   $7.3833   $7.38   $7.40   $7.40  
  7 purchase totals = $801.12       $854.6601   $854.66   $854.70   $854.70