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	$49.97	6.477%	$53.2066	$53.21	$53.20	$53.20
Purchase #2	$28.92	13.136%	$32.7189	$32.72	$32.70	$32.70
Purchase #3	$72.67	13.539%	$82.5088	$82.51	$82.50	$82.50
Purchase #4	$99.29	4.149%	$103.4095	$103.41	$103.40	$103.40
Purchase #5	$163.48	11.358%	$182.0481	$182.05	$182.05	$182.00
Purchase #6	$244.72	4.362%	$255.3947	$255.39	$255.40	$255.40
Purchase #7	$184.71	7.215%	$198.0368	$198.04	$198.05	$198.00
7 purchase totals =	$843.76		$907.3234	$907.33	$907.30	$907.20