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 $94.62   3.529%   $97.9591   $97.96   $97.95   $98.00  
  Purchase #2 $193.79   13.610%   $220.1648   $220.16   $220.15   $220.20  
  Purchase #3 $153.91   8.582%   $167.1186   $167.12   $167.10   $167.10  
  Purchase #4 $242.65   13.795%   $276.1236   $276.12   $276.10   $276.10  
  Purchase #5 $62.29   5.781%   $65.891   $65.89   $65.90   $65.90  
  Purchase #6 $7.98   6.149%   $8.4707   $8.47   $8.45   $8.50  
  Purchase #7 $69.57   9.669%   $76.2967   $76.30   $76.30   $76.30  
  7 purchase totals = $824.81       $912.0245   $912.02   $911.95   $912.10