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 $44.44   4.149%   $46.2838   $46.28   $46.30   $46.30  
  Purchase #2 $73.29   12.858%   $82.7136   $82.71   $82.70   $82.70  
  Purchase #3 $199.33   6.347%   $211.9815   $211.98   $212.00   $212.00  
  Purchase #4 $109.67   6.467%   $116.7624   $116.76   $116.75   $116.80  
  Purchase #5 $204.82   8.142%   $221.4964   $221.50   $221.50   $221.50  
  Purchase #6 $177.40   11.386%   $197.5988   $197.60   $197.60   $197.60  
  Purchase #7 $55.37   8.322%   $59.9779   $59.98   $60.00   $60.00  
  7 purchase totals = $864.32       $936.8144   $936.81   $936.85   $936.90