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 $57.59   5.790%   $60.9245   $60.92   $60.90   $60.90  
  Purchase #2 $211.91   10.810%   $234.8175   $234.82   $234.80   $234.80  
  Purchase #3 $70.95   7.745%   $76.4451   $76.45   $76.45   $76.40  
  Purchase #4 $16.25   11.211%   $18.0718   $18.07   $18.05   $18.10  
  Purchase #5 $244.26   6.465%   $260.0514   $260.05   $260.05   $260.10  
  Purchase #6 $218.94   4.602%   $229.0156   $229.02   $229.00   $229.00  
  Purchase #7 $164.31   11.367%   $182.9871   $182.99   $183.00   $183.00  
  7 purchase totals = $984.21       $1,062.3130   $1,062.32   $1,062.25   $1,062.30