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 $183.86   12.264%   $206.4086   $206.41   $206.40   $206.40  
  Purchase #2 $113.87   9.433%   $124.6114   $124.61   $124.60   $124.60  
  Purchase #3 $166.83   7.203%   $178.8468   $178.85   $178.85   $178.80  
  Purchase #4 $98.57   5.863%   $104.3492   $104.35   $104.35   $104.30  
  Purchase #5 $144.54   11.399%   $161.0161   $161.02   $161.00   $161.00  
  Purchase #6 $40.81   3.398%   $42.1967   $42.20   $42.20   $42.20  
  Purchase #7 $194.77   8.795%   $211.9   $211.90   $211.90   $211.90  
  7 purchase totals = $943.25       $1,029.3288   $1,029.34   $1,029.30   $1,029.20