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 $118.46   6.217%   $125.8247   $125.82   $125.80   $125.80  
  Purchase #2 $197.66   11.433%   $220.2585   $220.26   $220.25   $220.30  
  Purchase #3 $59.76   8.393%   $64.7757   $64.78   $64.80   $64.80  
  Purchase #4 $216.92   10.362%   $239.3973   $239.40   $239.40   $239.40  
  Purchase #5 $95.72   11.811%   $107.0255   $107.03   $107.05   $107.00  
  Purchase #6 $249.56   10.318%   $275.3096   $275.31   $275.30   $275.30  
  Purchase #7 $95.46   13.147%   $108.0101   $108.01   $108.00   $108.00  
  7 purchase totals = $1,033.54       $1,140.6014   $1,140.61   $1,140.60   $1,140.60