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	$144.44	7.533%	$155.3207	$155.32	$155.30	$155.30
Purchase #2	$113.46	10.662%	$125.5571	$125.56	$125.55	$125.60
Purchase #3	$14.34	13.809%	$16.3202	$16.32	$16.30	$16.30
Purchase #4	$80.55	11.104%	$89.4943	$89.49	$89.50	$89.50
Purchase #5	$144.43	13.203%	$163.4991	$163.50	$163.50	$163.50
Purchase #6	$113.56	4.364%	$118.5158	$118.52	$118.50	$118.50
Purchase #7	$36.43	4.145%	$37.94	$37.94	$37.95	$37.90
7 purchase totals =	$647.21		$706.6472	$706.65	$706.60	$706.60