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 $249.53   7.619%   $268.5417   $268.54   $268.55   $268.50  
  Purchase #2 $121.42   12.290%   $136.3425   $136.34   $136.35   $136.30  
  Purchase #3 $126.82   13.330%   $143.7251   $143.73   $143.75   $143.70  
  Purchase #4 $187.61   11.382%   $208.9638   $208.96   $208.95   $209.00  
  Purchase #5 $181.46   4.471%   $189.5731   $189.57   $189.55   $189.60  
  Purchase #6 $194.69   3.232%   $200.9824   $200.98   $201.00   $201.00  
  Purchase #7 $52.99   11.636%   $59.1559   $59.16   $59.15   $59.20  
  7 purchase totals = $1,114.52       $1,207.2845   $1,207.28   $1,207.30   $1,207.30