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 $122.63   11.338%   $136.5338   $136.53   $136.55   $136.50  
  Purchase #2 $172.74   13.464%   $195.9977   $196.00   $196.00   $196.00  
  Purchase #3 $26.28   12.164%   $29.4767   $29.48   $29.50   $29.50  
  Purchase #4 $244.44   7.578%   $262.9637   $262.96   $262.95   $263.00  
  Purchase #5 $132.58   12.628%   $149.3222   $149.32   $149.30   $149.30  
  Purchase #6 $174.70   10.204%   $192.5264   $192.53   $192.55   $192.50  
  Purchase #7 $104.64   5.533%   $110.4297   $110.43   $110.45   $110.40  
  7 purchase totals = $978.01       $1,077.2502   $1,077.25   $1,077.30   $1,077.20