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	$74.50	6.731%	$79.5146	$79.51	$79.50	$79.50
Purchase #2	$31.94	4.797%	$33.4722	$33.47	$33.45	$33.50
Purchase #3	$143.26	11.267%	$159.4011	$159.40	$159.40	$159.40
Purchase #4	$247.53	9.430%	$270.8721	$270.87	$270.85	$270.90
Purchase #5	$35.32	11.507%	$39.3843	$39.38	$39.40	$39.40
Purchase #6	$180.40	8.812%	$196.2968	$196.30	$196.30	$196.30
Purchase #7	$34.27	9.837%	$37.6411	$37.64	$37.65	$37.60
7 purchase totals =	$747.22		$816.5822	$816.57	$816.55	$816.60