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 $244.34   11.161%   $271.6108   $271.61   $271.60   $271.60  
  Purchase #2 $20.88   10.691%   $23.1123   $23.11   $23.10   $23.10  
  Purchase #3 $219.86   3.379%   $227.2891   $227.29   $227.30   $227.30  
  Purchase #4 $38.93   13.382%   $44.1396   $44.14   $44.15   $44.10  
  Purchase #5 $160.97   9.865%   $176.8497   $176.85   $176.85   $176.80  
  Purchase #6 $241.55   12.136%   $270.8645   $270.86   $270.85   $270.90  
  Purchase #7 $57.28   11.447%   $63.8368   $63.84   $63.85   $63.80  
  7 purchase totals = $983.81       $1,077.7028   $1,077.70   $1,077.70   $1,077.60