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 $244.50   12.197%   $274.3217   $274.32   $274.30   $274.30  
  Purchase #2 $242.48   5.558%   $255.957   $255.96   $255.95   $256.00  
  Purchase #3 $41.61   13.783%   $47.3451   $47.35   $47.35   $47.30  
  Purchase #4 $241.26   7.159%   $258.5318   $258.53   $258.55   $258.50  
  Purchase #5 $125.72   13.237%   $142.3616   $142.36   $142.35   $142.40  
  Purchase #6 $41.55   13.120%   $47.0014   $47.00   $47.00   $47.00  
  Purchase #7 $79.87   9.527%   $87.4792   $87.48   $87.50   $87.50  
  7 purchase totals = $1,016.99       $1,112.9978   $1,113.00   $1,113.00   $1,113.00