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 $199.51   12.613%   $224.6742   $224.67   $224.65   $224.70  
  Purchase #2 $55.81   3.489%   $57.7572   $57.76   $57.75   $57.80  
  Purchase #3 $221.28   11.109%   $245.862   $245.86   $245.85   $245.90  
  Purchase #4 $183.40   4.840%   $192.2766   $192.28   $192.30   $192.30  
  Purchase #5 $66.69   3.866%   $69.2682   $69.27   $69.25   $69.30  
  Purchase #6 $150.36   12.592%   $169.2933   $169.29   $169.30   $169.30  
  Purchase #7 $60.35   10.515%   $66.6958   $66.70   $66.70   $66.70  
  7 purchase totals = $937.40       $1,025.8273   $1,025.83   $1,025.80   $1,026.00