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 $53.38   8.543%   $57.9403   $57.94   $57.95   $57.90  
  Purchase #2 $107.84   10.124%   $118.7577   $118.76   $118.75   $118.80  
  Purchase #3 $33.56   9.757%   $36.8344   $36.83   $36.85   $36.80  
  Purchase #4 $172.66   10.315%   $190.4699   $190.47   $190.45   $190.50  
  Purchase #5 $128.73   4.847%   $134.9695   $134.97   $134.95   $135.00  
  Purchase #6 $120.33   8.586%   $130.6615   $130.66   $130.65   $130.70  
  Purchase #7 $40.85   9.212%   $44.6131   $44.61   $44.60   $44.60  
  7 purchase totals = $657.35       $714.2464   $714.24   $714.20   $714.30