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 $70.80   4.821%   $74.2133   $74.21   $74.20   $74.20  
  Purchase #2 $183.95   11.262%   $204.6664   $204.67   $204.65   $204.70  
  Purchase #3 $100.45   9.261%   $109.7527   $109.75   $109.75   $109.80  
  Purchase #4 $98.86   8.730%   $107.4905   $107.49   $107.50   $107.50  
  Purchase #5 $120.34   4.317%   $125.5351   $125.54   $125.55   $125.50  
  Purchase #6 $57.69   3.300%   $59.5938   $59.59   $59.60   $59.60  
  Purchase #7 $226.37   10.472%   $250.0755   $250.08   $250.10   $250.10  
  7 purchase totals = $858.46       $931.3273   $931.33   $931.35   $931.40