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 $64.33   8.844%   $70.0193   $70.02   $70.00   $70.00  
  Purchase #2 $152.78   11.560%   $170.4414   $170.44   $170.45   $170.40  
  Purchase #3 $34.75   5.537%   $36.6741   $36.67   $36.65   $36.70  
  Purchase #4 $76.98   12.469%   $86.5786   $86.58   $86.60   $86.60  
  Purchase #5 $117.87   5.291%   $124.1065   $124.11   $124.10   $124.10  
  Purchase #6 $69.49   6.403%   $73.9394   $73.94   $73.95   $73.90  
  Purchase #7 $100.69   11.658%   $112.4284   $112.43   $112.45   $112.40  
  7 purchase totals = $616.89       $674.1877   $674.19   $674.20   $674.10