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 $184.68   11.693%   $206.2746   $206.27   $206.25   $206.30  
  Purchase #2 $212.70   6.820%   $227.2061   $227.21   $227.20   $227.20  
  Purchase #3 $60.53   7.435%   $65.0304   $65.03   $65.05   $65.00  
  Purchase #4 $74.72   11.795%   $83.5332   $83.53   $83.55   $83.50  
  Purchase #5 $229.96   13.629%   $261.3012   $261.30   $261.30   $261.30  
  Purchase #6 $121.35   3.324%   $125.3837   $125.38   $125.40   $125.40  
  Purchase #7 $237.98   13.852%   $270.945   $270.95   $270.95   $270.90  
  7 purchase totals = $1,121.92       $1,239.6742   $1,239.67   $1,239.70   $1,239.60