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 $57.32   6.119%   $60.8274   $60.83   $60.85   $60.80  
  Purchase #2 $208.71   5.547%   $220.2871   $220.29   $220.30   $220.30  
  Purchase #3 $161.73   3.243%   $166.9749   $166.97   $166.95   $167.00  
  Purchase #4 $130.41   7.491%   $140.179   $140.18   $140.20   $140.20  
  Purchase #5 $207.74   8.782%   $225.9837   $225.98   $226.00   $226.00  
  Purchase #6 $48.74   13.840%   $55.4856   $55.49   $55.50   $55.50  
  Purchase #7 $161.83   10.527%   $178.8658   $178.87   $178.85   $178.90  
  7 purchase totals = $976.48       $1,048.6035   $1,048.61   $1,048.65   $1,048.70