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 $30.43   13.810%   $34.6324   $34.63   $34.65   $34.60  
  Purchase #2 $127.89   3.852%   $132.8163   $132.82   $132.80   $132.80  
  Purchase #3 $38.72   5.602%   $40.8891   $40.89   $40.90   $40.90  
  Purchase #4 $204.57   10.486%   $226.0212   $226.02   $226.00   $226.00  
  Purchase #5 $102.48   11.764%   $114.5357   $114.54   $114.55   $114.50  
  Purchase #6 $237.51   9.369%   $259.7623   $259.76   $259.75   $259.80  
  Purchase #7 $63.63   3.283%   $65.719   $65.72   $65.70   $65.70  
  7 purchase totals = $805.23       $874.3760   $874.38   $874.35   $874.30