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 $60.98   13.674%   $69.3184   $69.32   $69.30   $69.30  
  Purchase #2 $173.34   8.241%   $187.6249   $187.62   $187.60   $187.60  
  Purchase #3 $202.95   5.122%   $213.3451   $213.35   $213.35   $213.30  
  Purchase #4 $134.33   12.626%   $151.2905   $151.29   $151.30   $151.30  
  Purchase #5 $232.87   7.859%   $251.1713   $251.17   $251.15   $251.20  
  Purchase #6 $56.57   12.119%   $63.4257   $63.43   $63.45   $63.40  
  Purchase #7 $157.40   3.636%   $163.1231   $163.12   $163.10   $163.10  
  7 purchase totals = $1,018.44       $1,099.2990   $1,099.30   $1,099.25   $1,099.20