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 $104.44   9.211%   $114.06   $114.06   $114.05   $114.10  
  Purchase #2 $76.93   13.853%   $87.5871   $87.59   $87.60   $87.60  
  Purchase #3 $81.78   11.402%   $91.1046   $91.10   $91.10   $91.10  
  Purchase #4 $165.79   10.519%   $183.2295   $183.23   $183.25   $183.20  
  Purchase #5 $63.62   13.142%   $71.9809   $71.98   $72.00   $72.00  
  Purchase #6 $151.96   12.193%   $170.4885   $170.49   $170.50   $170.50  
  Purchase #7 $152.97   10.353%   $168.807   $168.81   $168.80   $168.80  
  7 purchase totals = $797.49       $887.2576   $887.26   $887.30   $887.30