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	$71.62	4.555%	$74.8823	$74.88	$74.90	$74.90
Purchase #2	$82.64	3.476%	$85.5126	$85.51	$85.50	$85.50
Purchase #3	$87.38	13.611%	$99.2733	$99.27	$99.25	$99.30
Purchase #4	$157.65	10.686%	$174.4965	$174.50	$174.50	$174.50
Purchase #5	$226.48	10.609%	$250.5073	$250.51	$250.50	$250.50
Purchase #6	$55.63	3.529%	$57.5932	$57.59	$57.60	$57.60
Purchase #7	$73.42	4.176%	$76.486	$76.49	$76.50	$76.50
7 purchase totals =	$754.82		$818.7512	$818.75	$818.75	$818.80