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 $239.62   9.219%   $261.7106   $261.71   $261.70   $261.70  
  Purchase #2 $157.53   7.618%   $169.5306   $169.53   $169.55   $169.50  
  Purchase #3 $193.35   6.136%   $205.214   $205.21   $205.20   $205.20  
  Purchase #4 $16.79   6.374%   $17.8602   $17.86   $17.85   $17.90  
  Purchase #5 $100.97   10.549%   $111.6213   $111.62   $111.60   $111.60  
  Purchase #6 $38.77   13.485%   $43.9981   $44.00   $44.00   $44.00  
  Purchase #7 $127.77   13.701%   $145.2758   $145.28   $145.30   $145.30  
  7 purchase totals = $874.80       $955.2106   $955.21   $955.20   $955.20