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 $38.83   10.799%   $43.0233   $43.02   $43.00   $43.00  
  Purchase #2 $243.54   3.147%   $251.2042   $251.20   $251.20   $251.20  
  Purchase #3 $68.43   6.566%   $72.9231   $72.92   $72.90   $72.90  
  Purchase #4 $224.80   8.866%   $244.7308   $244.73   $244.75   $244.70  
  Purchase #5 $67.92   13.183%   $76.8739   $76.87   $76.85   $76.90  
  Purchase #6 $240.73   13.828%   $274.0181   $274.02   $274.00   $274.00  
  Purchase #7 $184.59   10.637%   $204.2248   $204.22   $204.20   $204.20  
  7 purchase totals = $1,068.84       $1,166.9982   $1,166.98   $1,166.90   $1,166.90