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 $223.77   12.162%   $250.9849   $250.98   $251.00   $251.00  
  Purchase #2 $152.70   13.391%   $173.1481   $173.15   $173.15   $173.10  
  Purchase #3 $235.38   4.836%   $246.763   $246.76   $246.75   $246.80  
  Purchase #4 $185.36   11.352%   $206.4021   $206.40   $206.40   $206.40  
  Purchase #5 $214.43   12.637%   $241.5275   $241.53   $241.55   $241.50  
  Purchase #6 $26.74   8.207%   $28.9346   $28.93   $28.95   $28.90  
  Purchase #7 $53.28   5.622%   $56.2754   $56.28   $56.30   $56.30  
  7 purchase totals = $1,091.66       $1,204.0356   $1,204.03   $1,204.10   $1,204.00