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 $65.82   8.814%   $71.6214   $71.62   $71.60   $71.60  
  Purchase #2 $15.31   7.147%   $16.4042   $16.40   $16.40   $16.40  
  Purchase #3 $68.53   3.152%   $70.6901   $70.69   $70.70   $70.70  
  Purchase #4 $121.65   8.744%   $132.2871   $132.29   $132.30   $132.30  
  Purchase #5 $54.34   11.675%   $60.6842   $60.68   $60.70   $60.70  
  Purchase #6 $244.57   7.237%   $262.2695   $262.27   $262.25   $262.30  
  Purchase #7 $229.66   8.425%   $249.0089   $249.01   $249.00   $249.00  
  7 purchase totals = $799.88       $862.9654   $862.96   $862.95   $863.00