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 $204.41   6.417%   $217.527   $217.53   $217.55   $217.50  
  Purchase #2 $117.48   13.149%   $132.9274   $132.93   $132.95   $132.90  
  Purchase #3 $52.49   4.371%   $54.7843   $54.78   $54.80   $54.80  
  Purchase #4 $237.87   3.423%   $246.0123   $246.01   $246.00   $246.00  
  Purchase #5 $141.30   7.716%   $152.2027   $152.20   $152.20   $152.20  
  Purchase #6 $59.34   10.238%   $65.4152   $65.42   $65.40   $65.40  
  Purchase #7 $180.43   9.579%   $197.7134   $197.71   $197.70   $197.70  
  7 purchase totals = $993.32       $1,066.5823   $1,066.58   $1,066.60   $1,066.50