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 $206.48   8.652%   $224.3446   $224.34   $224.35   $224.30  
  Purchase #2 $35.98   5.259%   $37.8722   $37.87   $37.85   $37.90  
  Purchase #3 $224.98   6.317%   $239.192   $239.19   $239.20   $239.20  
  Purchase #4 $239.73   8.381%   $259.8218   $259.82   $259.80   $259.80  
  Purchase #5 $212.95   13.594%   $241.8984   $241.90   $241.90   $241.90  
  Purchase #6 $244.93   6.779%   $261.5338   $261.53   $261.55   $261.50  
  Purchase #7 $198.41   10.665%   $219.5704   $219.57   $219.55   $219.60  
  7 purchase totals = $1,363.46       $1,484.2332   $1,484.22   $1,484.20   $1,484.20