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	$6.73	7.522%	$7.2362	$7.24	$7.25	$7.20
Purchase #2	$140.52	7.113%	$150.5152	$150.52	$150.50	$150.50
Purchase #3	$48.61	6.469%	$51.7546	$51.75	$51.75	$51.80
Purchase #4	$37.31	13.588%	$42.3797	$42.38	$42.40	$42.40
Purchase #5	$184.97	9.609%	$202.7438	$202.74	$202.75	$202.70
Purchase #6	$67.40	4.459%	$70.4054	$70.41	$70.40	$70.40
Purchase #7	$6.53	13.509%	$7.4121	$7.41	$7.40	$7.40
7 purchase totals =	$492.07		$532.4470	$532.45	$532.45	$532.40