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 $219.50   11.641%   $245.052   $245.05   $245.05   $245.10  
  Purchase #2 $29.59   12.444%   $33.2722   $33.27   $33.25   $33.30  
  Purchase #3 $19.94   13.390%   $22.61   $22.61   $22.60   $22.60  
  Purchase #4 $201.37   4.862%   $211.1606   $211.16   $211.15   $211.20  
  Purchase #5 $63.84   3.673%   $66.1848   $66.18   $66.20   $66.20  
  Purchase #6 $141.88   8.504%   $153.9455   $153.95   $153.95   $153.90  
  Purchase #7 $211.29   11.871%   $236.3722   $236.37   $236.35   $236.40  
  7 purchase totals = $887.41       $968.5973   $968.59   $968.55   $968.70