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 $190.74   6.542%   $203.2182   $203.22   $203.20   $203.20  
  Purchase #2 $176.71   11.257%   $196.6022   $196.60   $196.60   $196.60  
  Purchase #3 $140.79   13.854%   $160.295   $160.30   $160.30   $160.30  
  Purchase #4 $239.68   8.602%   $260.2973   $260.30   $260.30   $260.30  
  Purchase #5 $238.86   6.225%   $253.729   $253.73   $253.75   $253.70  
  Purchase #6 $193.58   10.861%   $214.6047   $214.60   $214.60   $214.60  
  Purchase #7 $229.29   10.793%   $254.0373   $254.04   $254.05   $254.00  
  7 purchase totals = $1,409.65       $1,542.7837   $1,542.79   $1,542.80   $1,542.70