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 $62.60   3.808%   $64.9838   $64.98   $65.00   $65.00  
  Purchase #2 $152.78   6.306%   $162.4143   $162.41   $162.40   $162.40  
  Purchase #3 $250.87   13.857%   $285.6331   $285.63   $285.65   $285.60  
  Purchase #4 $191.49   7.241%   $205.3558   $205.36   $205.35   $205.40  
  Purchase #5 $207.69   9.632%   $227.6947   $227.69   $227.70   $227.70  
  Purchase #6 $158.82   12.271%   $178.3088   $178.31   $178.30   $178.30  
  Purchase #7 $83.83   3.300%   $86.5964   $86.60   $86.60   $86.60  
  7 purchase totals = $1,108.08       $1,210.9869   $1,210.98   $1,211.00   $1,211.00