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 $168.99   11.361%   $188.189   $188.19   $188.20   $188.20  
  Purchase #2 $28.62   10.560%   $31.6423   $31.64   $31.65   $31.60  
  Purchase #3 $33.94   6.793%   $36.2455   $36.25   $36.25   $36.20  
  Purchase #4 $86.70   5.687%   $91.6306   $91.63   $91.65   $91.60  
  Purchase #5 $132.94   10.832%   $147.3401   $147.34   $147.35   $147.30  
  Purchase #6 $40.77   10.241%   $44.9453   $44.95   $44.95   $44.90  
  Purchase #7 $163.46   11.359%   $182.0274   $182.03   $182.05   $182.00  
  7 purchase totals = $655.42       $722.0202   $722.03   $722.10   $721.80