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 $232.73   7.527%   $250.2476   $250.25   $250.25   $250.20  
  Purchase #2 $236.42   8.513%   $256.5464   $256.55   $256.55   $256.50  
  Purchase #3 $36.84   7.758%   $39.698   $39.70   $39.70   $39.70  
  Purchase #4 $244.78   8.305%   $265.109   $265.11   $265.10   $265.10  
  Purchase #5 $205.56   12.600%   $231.4606   $231.46   $231.45   $231.50  
  Purchase #6 $200.68   7.472%   $215.6748   $215.67   $215.65   $215.70  
  Purchase #7 $33.79   9.425%   $36.9747   $36.97   $36.95   $37.00  
  7 purchase totals = $1,190.80       $1,295.7111   $1,295.71   $1,295.65   $1,295.70