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 $119.34   8.503%   $129.4875   $129.49   $129.50   $129.50  
  Purchase #2 $178.46   9.614%   $195.6171   $195.62   $195.60   $195.60  
  Purchase #3 $245.30   13.201%   $277.6821   $277.68   $277.70   $277.70  
  Purchase #4 $58.38   10.173%   $64.319   $64.32   $64.30   $64.30  
  Purchase #5 $196.46   9.675%   $215.4675   $215.47   $215.45   $215.50  
  Purchase #6 $90.32   6.297%   $96.0075   $96.01   $96.00   $96.00  
  Purchase #7 $240.57   11.215%   $267.5499   $267.55   $267.55   $267.50  
  7 purchase totals = $1,128.83       $1,246.1306   $1,246.14   $1,246.10   $1,246.10