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 $217.97   6.718%   $232.6132   $232.61   $232.60   $232.60  
  Purchase #2 $204.89   13.346%   $232.2346   $232.23   $232.25   $232.20  
  Purchase #3 $55.34   7.662%   $59.5802   $59.58   $59.60   $59.60  
  Purchase #4 $180.60   7.216%   $193.6321   $193.63   $193.65   $193.60  
  Purchase #5 $212.45   13.318%   $240.7441   $240.74   $240.75   $240.70  
  Purchase #6 $68.45   10.520%   $75.6509   $75.65   $75.65   $75.70  
  Purchase #7 $225.71   9.778%   $247.7799   $247.78   $247.80   $247.80  
  7 purchase totals = $1,165.41       $1,282.2350   $1,282.22   $1,282.30   $1,282.20