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 $121.78   3.712%   $126.3005   $126.30   $126.30   $126.30  
  Purchase #2 $31.39   4.155%   $32.6943   $32.69   $32.70   $32.70  
  Purchase #3 $147.35   8.695%   $160.1621   $160.16   $160.15   $160.20  
  Purchase #4 $232.83   11.468%   $259.5309   $259.53   $259.55   $259.50  
  Purchase #5 $20.54   5.643%   $21.6991   $21.70   $21.70   $21.70  
  Purchase #6 $250.69   4.857%   $262.866   $262.87   $262.85   $262.90  
  Purchase #7 $239.34   13.262%   $271.0813   $271.08   $271.10   $271.10  
  7 purchase totals = $1,043.92       $1,134.3342   $1,134.33   $1,134.35   $1,134.40