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 $208.83   6.505%   $222.4144   $222.41   $222.40   $222.40  
  Purchase #2 $204.99   3.160%   $211.4677   $211.47   $211.45   $211.50  
  Purchase #3 $85.29   11.357%   $94.9764   $94.98   $95.00   $95.00  
  Purchase #4 $236.79   4.322%   $247.0241   $247.02   $247.00   $247.00  
  Purchase #5 $107.74   6.382%   $114.616   $114.62   $114.60   $114.60  
  Purchase #6 $82.59   10.619%   $91.3602   $91.36   $91.35   $91.40  
  Purchase #7 $246.33   11.180%   $273.8697   $273.87   $273.85   $273.90  
  7 purchase totals = $1,172.56       $1,255.7285   $1,255.73   $1,255.65   $1,255.80