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 $63.66   12.166%   $71.4049   $71.40   $71.40   $71.40  
  Purchase #2 $108.98   4.585%   $113.9767   $113.98   $114.00   $114.00  
  Purchase #3 $107.27   3.843%   $111.3924   $111.39   $111.40   $111.40  
  Purchase #4 $192.55   9.874%   $211.5624   $211.56   $211.55   $211.60  
  Purchase #5 $74.98   6.668%   $79.9797   $79.98   $80.00   $80.00  
  Purchase #6 $57.57   12.670%   $64.8641   $64.86   $64.85   $64.90  
  Purchase #7 $233.74   10.607%   $258.5328   $258.53   $258.55   $258.50  
  7 purchase totals = $838.75       $911.7130   $911.70   $911.75   $911.80