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 $246.62   8.516%   $267.6222   $267.62   $267.60   $267.60  
  Purchase #2 $137.96   8.660%   $149.9073   $149.91   $149.90   $149.90  
  Purchase #3 $114.92   3.207%   $118.6055   $118.61   $118.60   $118.60  
  Purchase #4 $19.84   4.787%   $20.7897   $20.79   $20.80   $20.80  
  Purchase #5 $85.37   12.424%   $95.9764   $95.98   $96.00   $96.00  
  Purchase #6 $85.64   8.303%   $92.7507   $92.75   $92.75   $92.80  
  Purchase #7 $54.54   10.184%   $60.0944   $60.09   $60.10   $60.10  
  7 purchase totals = $744.89       $805.7462   $805.75   $805.75   $805.80