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 $51.67   9.342%   $56.497   $56.50   $56.50   $56.50  
  Purchase #2 $86.50   6.708%   $92.3024   $92.30   $92.30   $92.30  
  Purchase #3 $218.51   8.414%   $236.8954   $236.90   $236.90   $236.90  
  Purchase #4 $147.91   10.846%   $163.9523   $163.95   $163.95   $164.00  
  Purchase #5 $79.61   6.510%   $84.7926   $84.79   $84.80   $84.80  
  Purchase #6 $199.50   5.203%   $209.88   $209.88   $209.90   $209.90  
  Purchase #7 $239.83   3.248%   $247.6197   $247.62   $247.60   $247.60  
  7 purchase totals = $1,023.53       $1,091.9394   $1,091.94   $1,091.95   $1,092.00