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 $61.82   10.595%   $68.3698   $68.37   $68.35   $68.40  
  Purchase #2 $82.41   4.330%   $85.9784   $85.98   $86.00   $86.00  
  Purchase #3 $112.96   3.308%   $116.6967   $116.70   $116.70   $116.70  
  Purchase #4 $207.43   6.689%   $221.305   $221.31   $221.30   $221.30  
  Purchase #5 $210.60   3.822%   $218.6491   $218.65   $218.65   $218.60  
  Purchase #6 $150.93   4.491%   $157.7083   $157.71   $157.70   $157.70  
  Purchase #7 $121.99   8.777%   $132.6971   $132.70   $132.70   $132.70  
  7 purchase totals = $948.14       $1,001.4044   $1,001.42   $1,001.40   $1,001.40