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 $188.42   8.792%   $204.9859   $204.99   $205.00   $205.00  
  Purchase #2 $150.99   5.469%   $159.2476   $159.25   $159.25   $159.20  
  Purchase #3 $87.77   13.800%   $99.8823   $99.88   $99.90   $99.90  
  Purchase #4 $183.92   10.749%   $203.6896   $203.69   $203.70   $203.70  
  Purchase #5 $101.57   11.420%   $113.1693   $113.17   $113.15   $113.20  
  Purchase #6 $95.87   5.853%   $101.4813   $101.48   $101.50   $101.50  
  Purchase #7 $134.60   10.516%   $148.7545   $148.75   $148.75   $148.80  
  7 purchase totals = $943.14       $1,031.2105   $1,031.21   $1,031.25   $1,031.30