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 $204.77   10.122%   $225.4968   $225.50   $225.50   $225.50  
  Purchase #2 $111.86   7.149%   $119.8569   $119.86   $119.85   $119.90  
  Purchase #3 $111.42   4.436%   $116.3626   $116.36   $116.35   $116.40  
  Purchase #4 $89.64   9.736%   $98.3674   $98.37   $98.35   $98.40  
  Purchase #5 $91.95   3.432%   $95.1057   $95.11   $95.10   $95.10  
  Purchase #6 $158.50   6.758%   $169.2114   $169.21   $169.20   $169.20  
  Purchase #7 $184.81   11.384%   $205.8488   $205.85   $205.85   $205.80  
  7 purchase totals = $952.95       $1,030.2496   $1,030.26   $1,030.20   $1,030.30