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 $169.83   8.748%   $184.6867   $184.69   $184.70   $184.70  
  Purchase #2 $54.77   7.674%   $58.973   $58.97   $58.95   $59.00  
  Purchase #3 $237.34   3.712%   $246.1501   $246.15   $246.15   $246.20  
  Purchase #4 $36.35   5.596%   $38.3841   $38.38   $38.40   $38.40  
  Purchase #5 $231.58   6.314%   $246.202   $246.20   $246.20   $246.20  
  Purchase #6 $17.64   10.138%   $19.4283   $19.43   $19.45   $19.40  
  Purchase #7 $62.32   13.808%   $70.9251   $70.93   $70.95   $70.90  
  7 purchase totals = $809.83       $864.7493   $864.75   $864.80   $864.80