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 $131.38   10.116%   $144.6704   $144.67   $144.65   $144.70  
  Purchase #2 $195.43   12.543%   $219.9428   $219.94   $219.95   $219.90  
  Purchase #3 $55.57   12.444%   $62.4851   $62.49   $62.50   $62.50  
  Purchase #4 $66.43   9.526%   $72.7581   $72.76   $72.75   $72.80  
  Purchase #5 $55.37   3.685%   $57.4104   $57.41   $57.40   $57.40  
  Purchase #6 $70.84   5.591%   $74.8007   $74.80   $74.80   $74.80  
  Purchase #7 $125.69   5.867%   $133.0642   $133.06   $133.05   $133.10  
  7 purchase totals = $700.71       $765.1317   $765.13   $765.10   $765.20