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 $94.34   4.325%   $98.4202   $98.42   $98.40   $98.40  
  Purchase #2 $172.81   11.341%   $192.4084   $192.41   $192.40   $192.40  
  Purchase #3 $250.31   6.556%   $266.7203   $266.72   $266.70   $266.70  
  Purchase #4 $233.38   4.859%   $244.7199   $244.72   $244.70   $244.70  
  Purchase #5 $247.64   11.381%   $275.8239   $275.82   $275.80   $275.80  
  Purchase #6 $218.62   8.592%   $237.4038   $237.40   $237.40   $237.40  
  Purchase #7 $110.64   8.711%   $120.2779   $120.28   $120.30   $120.30  
  7 purchase totals = $1,327.74       $1,435.7744   $1,435.77   $1,435.70   $1,435.70