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 $86.31   13.785%   $98.2078   $98.21   $98.20   $98.20  
  Purchase #2 $230.34   10.233%   $253.9107   $253.91   $253.90   $253.90  
  Purchase #3 $152.64   7.262%   $163.7247   $163.72   $163.70   $163.70  
  Purchase #4 $96.77   9.312%   $105.7812   $105.78   $105.80   $105.80  
  Purchase #5 $213.48   6.524%   $227.4074   $227.41   $227.40   $227.40  
  Purchase #6 $134.82   9.367%   $147.4486   $147.45   $147.45   $147.40  
  Purchase #7 $137.72   12.842%   $155.406   $155.41   $155.40   $155.40  
  7 purchase totals = $1,052.08       $1,151.8864   $1,151.89   $1,151.85   $1,151.80