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 $125.76   9.434%   $137.6242   $137.62   $137.60   $137.60  
  Purchase #2 $65.70   12.414%   $73.856   $73.86   $73.85   $73.90  
  Purchase #3 $79.92   9.715%   $87.6842   $87.68   $87.70   $87.70  
  Purchase #4 $226.35   8.381%   $245.3204   $245.32   $245.30   $245.30  
  Purchase #5 $50.42   6.714%   $53.8052   $53.81   $53.80   $53.80  
  Purchase #6 $241.27   13.706%   $274.3385   $274.34   $274.35   $274.30  
  Purchase #7 $34.69   12.456%   $39.011   $39.01   $39.00   $39.00  
  7 purchase totals = $824.11       $911.6395   $911.64   $911.60   $911.60