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 $235.44   11.724%   $263.043   $263.04   $263.05   $263.00  
  Purchase #2 $231.43   3.519%   $239.574   $239.57   $239.55   $239.60  
  Purchase #3 $83.98   5.325%   $88.4519   $88.45   $88.45   $88.50  
  Purchase #4 $225.34   11.218%   $250.6186   $250.62   $250.60   $250.60  
  Purchase #5 $225.87   10.396%   $249.3514   $249.35   $249.35   $249.40  
  Purchase #6 $224.94   13.325%   $254.9133   $254.91   $254.90   $254.90  
  Purchase #7 $67.78   7.709%   $73.0052   $73.01   $73.00   $73.00  
  7 purchase totals = $1,294.78       $1,418.9574   $1,418.95   $1,418.90   $1,419.00