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 $192.50   6.433%   $204.8835   $204.88   $204.90   $204.90  
  Purchase #2 $15.62   12.708%   $17.605   $17.61   $17.60   $17.60  
  Purchase #3 $235.66   3.525%   $243.967   $243.97   $243.95   $244.00  
  Purchase #4 $227.63   8.842%   $247.757   $247.76   $247.75   $247.80  
  Purchase #5 $90.70   13.828%   $103.242   $103.24   $103.25   $103.20  
  Purchase #6 $214.49   12.721%   $241.7753   $241.78   $241.80   $241.80  
  Purchase #7 $9.64   9.211%   $10.5279   $10.53   $10.55   $10.50  
  7 purchase totals = $986.24       $1,069.7577   $1,069.77   $1,069.80   $1,069.80