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 $32.98   8.722%   $35.8565   $35.86   $35.85   $35.90  
  Purchase #2 $207.58   10.729%   $229.8513   $229.85   $229.85   $229.90  
  Purchase #3 $95.32   10.737%   $105.5545   $105.55   $105.55   $105.60  
  Purchase #4 $114.35   7.205%   $122.5889   $122.59   $122.60   $122.60  
  Purchase #5 $206.28   7.429%   $221.6045   $221.60   $221.60   $221.60  
  Purchase #6 $6.42   11.457%   $7.1555   $7.16   $7.15   $7.20  
  Purchase #7 $147.50   9.375%   $161.3281   $161.33   $161.35   $161.30  
  7 purchase totals = $810.43       $883.9393   $883.94   $883.95   $884.10