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 $236.29   13.820%   $268.9453   $268.95   $268.95   $268.90  
  Purchase #2 $121.63   8.718%   $132.2337   $132.23   $132.25   $132.20  
  Purchase #3 $16.37   9.706%   $17.9589   $17.96   $17.95   $18.00  
  Purchase #4 $247.89   4.170%   $258.227   $258.23   $258.25   $258.20  
  Purchase #5 $43.86   4.842%   $45.9837   $45.98   $46.00   $46.00  
  Purchase #6 $184.49   13.115%   $208.6859   $208.69   $208.70   $208.70  
  Purchase #7 $219.50   8.260%   $237.6307   $237.63   $237.65   $237.60  
  7 purchase totals = $1,070.03       $1,169.6652   $1,169.67   $1,169.75   $1,169.60