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 $95.54   3.591%   $98.9708   $98.97   $98.95   $99.00  
  Purchase #2 $189.41   5.294%   $199.4374   $199.44   $199.45   $199.40  
  Purchase #3 $7.91   9.406%   $8.654   $8.65   $8.65   $8.70  
  Purchase #4 $46.39   11.803%   $51.8654   $51.87   $51.85   $51.90  
  Purchase #5 $234.53   4.129%   $244.2137   $244.21   $244.20   $244.20  
  Purchase #6 $81.62   13.112%   $92.322   $92.32   $92.30   $92.30  
  Purchase #7 $75.72   10.591%   $83.7395   $83.74   $83.75   $83.70  
  7 purchase totals = $731.12       $779.2028   $779.20   $779.15   $779.20