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 $158.53   6.610%   $169.0088   $169.01   $169.00   $169.00  
  Purchase #2 $147.57   3.563%   $152.8279   $152.83   $152.85   $152.80  
  Purchase #3 $19.81   4.517%   $20.7048   $20.70   $20.70   $20.70  
  Purchase #4 $56.89   3.294%   $58.764   $58.76   $58.75   $58.80  
  Purchase #5 $77.68   10.237%   $85.6321   $85.63   $85.65   $85.60  
  Purchase #6 $92.73   5.856%   $98.1603   $98.16   $98.15   $98.20  
  Purchase #7 $241.63   6.784%   $258.0222   $258.02   $258.00   $258.00  
  7 purchase totals = $794.84       $843.1201   $843.11   $843.10   $843.10