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 $147.29   13.507%   $167.1845   $167.18   $167.20   $167.20  
  Purchase #2 $105.37   13.813%   $119.9248   $119.92   $119.90   $119.90  
  Purchase #3 $12.46   7.755%   $13.4263   $13.43   $13.45   $13.40  
  Purchase #4 $198.29   8.355%   $214.8571   $214.86   $214.85   $214.90  
  Purchase #5 $93.25   5.669%   $98.5363   $98.54   $98.55   $98.50  
  Purchase #6 $250.53   6.614%   $267.1001   $267.10   $267.10   $267.10  
  Purchase #7 $29.95   10.324%   $33.042   $33.04   $33.05   $33.00  
  7 purchase totals = $837.14       $914.0711   $914.07   $914.10   $914.00