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 $159.66   4.652%   $167.0874   $167.09   $167.10   $167.10  
  Purchase #2 $220.61   5.481%   $232.7016   $232.70   $232.70   $232.70  
  Purchase #3 $162.52   13.534%   $184.5155   $184.52   $184.50   $184.50  
  Purchase #4 $242.48   4.448%   $253.2655   $253.27   $253.25   $253.30  
  Purchase #5 $14.66   4.761%   $15.358   $15.36   $15.35   $15.40  
  Purchase #6 $102.81   13.347%   $116.5321   $116.53   $116.55   $116.50  
  Purchase #7 $57.94   11.312%   $64.4942   $64.49   $64.50   $64.50  
  7 purchase totals = $960.68       $1,033.9543   $1,033.96   $1,033.95   $1,034.00