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 $243.71   6.379%   $259.2563   $259.26   $259.25   $259.30  
  Purchase #2 $85.44   7.319%   $91.6934   $91.69   $91.70   $91.70  
  Purchase #3 $234.48   7.387%   $251.801   $251.80   $251.80   $251.80  
  Purchase #4 $117.84   4.501%   $123.144   $123.14   $123.15   $123.10  
  Purchase #5 $119.93   10.486%   $132.5059   $132.51   $132.50   $132.50  
  Purchase #6 $23.36   7.534%   $25.1199   $25.12   $25.10   $25.10  
  Purchase #7 $97.78   4.477%   $102.1576   $102.16   $102.15   $102.20  
  7 purchase totals = $922.54       $985.6781   $985.68   $985.65   $985.70