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 $62.81   13.102%   $71.0394   $71.04   $71.05   $71.00  
  Purchase #2 $44.99   3.104%   $46.3865   $46.39   $46.40   $46.40  
  Purchase #3 $29.46   9.615%   $32.2926   $32.29   $32.30   $32.30  
  Purchase #4 $76.63   5.407%   $80.7734   $80.77   $80.75   $80.80  
  Purchase #5 $209.26   11.588%   $233.509   $233.51   $233.50   $233.50  
  Purchase #6 $112.27   6.851%   $119.9616   $119.96   $119.95   $120.00  
  Purchase #7 $22.65   5.198%   $23.8273   $23.83   $23.85   $23.80  
  7 purchase totals = $558.07       $607.7898   $607.79   $607.80   $607.80