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 $187.61   11.745%   $209.6448   $209.64   $209.65   $209.60  
  Purchase #2 $226.51   10.795%   $250.9618   $250.96   $250.95   $251.00  
  Purchase #3 $246.28   6.297%   $261.7883   $261.79   $261.80   $261.80  
  Purchase #4 $140.91   8.505%   $152.8944   $152.89   $152.90   $152.90  
  Purchase #5 $204.74   3.748%   $212.4137   $212.41   $212.40   $212.40  
  Purchase #6 $76.82   9.194%   $83.8828   $83.88   $83.90   $83.90  
  Purchase #7 $58.86   12.707%   $66.3393   $66.34   $66.35   $66.30  
  7 purchase totals = $1,141.73       $1,237.9251   $1,237.91   $1,237.95   $1,237.90