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 $188.50   9.796%   $206.9655   $206.97   $206.95   $207.00  
  Purchase #2 $169.51   12.805%   $191.2158   $191.22   $191.20   $191.20  
  Purchase #3 $231.76   6.393%   $246.5764   $246.58   $246.60   $246.60  
  Purchase #4 $37.51   12.771%   $42.3004   $42.30   $42.30   $42.30  
  Purchase #5 $202.79   3.645%   $210.1817   $210.18   $210.20   $210.20  
  Purchase #6 $233.68   4.836%   $244.9808   $244.98   $245.00   $245.00  
  Purchase #7 $169.49   7.667%   $182.4848   $182.48   $182.50   $182.50  
  7 purchase totals = $1,233.24       $1,324.7054   $1,324.71   $1,324.75   $1,324.80