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 $65.97   13.752%   $75.0422   $75.04   $75.05   $75.00  
  Purchase #2 $248.67   12.787%   $280.4674   $280.47   $280.45   $280.50  
  Purchase #3 $192.93   8.494%   $209.3175   $209.32   $209.30   $209.30  
  Purchase #4 $212.98   7.693%   $229.3646   $229.36   $229.35   $229.40  
  Purchase #5 $163.70   4.481%   $171.0354   $171.04   $171.05   $171.00  
  Purchase #6 $236.44   11.350%   $263.2759   $263.28   $263.30   $263.30  
  Purchase #7 $29.93   8.483%   $32.469   $32.47   $32.45   $32.50  
  7 purchase totals = $1,150.62       $1,260.9720   $1,260.98   $1,260.95   $1,261.00