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 $224.80   10.865%   $249.2245   $249.22   $249.20   $249.20  
  Purchase #2 $224.43   3.438%   $232.1459   $232.15   $232.15   $232.10  
  Purchase #3 $56.74   5.518%   $59.8709   $59.87   $59.85   $59.90  
  Purchase #4 $62.56   5.453%   $65.9714   $65.97   $65.95   $66.00  
  Purchase #5 $198.67   8.463%   $215.4834   $215.48   $215.50   $215.50  
  Purchase #6 $14.62   12.327%   $16.4222   $16.42   $16.40   $16.40  
  Purchase #7 $161.55   8.651%   $175.5257   $175.53   $175.55   $175.50  
  7 purchase totals = $943.37       $1,014.6440   $1,014.64   $1,014.60   $1,014.60