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 $8.81   6.438%   $9.3772   $9.38   $9.40   $9.40  
  Purchase #2 $20.25   9.603%   $22.1946   $22.19   $22.20   $22.20  
  Purchase #3 $186.87   5.561%   $197.2618   $197.26   $197.25   $197.30  
  Purchase #4 $181.78   11.358%   $202.4266   $202.43   $202.45   $202.40  
  Purchase #5 $78.39   10.207%   $86.3913   $86.39   $86.40   $86.40  
  Purchase #6 $203.87   5.152%   $214.3734   $214.37   $214.35   $214.40  
  Purchase #7 $5.44   5.284%   $5.7274   $5.73   $5.75   $5.70  
  7 purchase totals = $685.41       $737.7523   $737.75   $737.80   $737.80