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 $67.58   8.236%   $73.1459   $73.15   $73.15   $73.10  
  Purchase #2 $48.29   11.294%   $53.7439   $53.74   $53.75   $53.70  
  Purchase #3 $151.79   6.375%   $161.4666   $161.47   $161.45   $161.50  
  Purchase #4 $86.92   10.240%   $95.8206   $95.82   $95.80   $95.80  
  Purchase #5 $219.46   7.154%   $235.1602   $235.16   $235.15   $235.20  
  Purchase #6 $198.62   5.415%   $209.3753   $209.38   $209.40   $209.40  
  Purchase #7 $117.31   9.352%   $128.2808   $128.28   $128.30   $128.30  
  7 purchase totals = $889.97       $956.9933   $957.00   $957.00   $957.00