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	$122.61	5.620%	$129.5007	$129.50	$129.50	$129.50
Purchase #2	$89.54	6.281%	$95.164	$95.16	$95.15	$95.20
Purchase #3	$54.45	11.390%	$60.6519	$60.65	$60.65	$60.70
Purchase #4	$95.77	4.113%	$99.709	$99.71	$99.70	$99.70
Purchase #5	$89.73	6.692%	$95.7347	$95.73	$95.75	$95.70
Purchase #6	$67.86	6.205%	$72.0707	$72.07	$72.05	$72.10
Purchase #7	$219.29	9.674%	$240.5041	$240.50	$240.50	$240.50
7 purchase totals =	$739.25		$793.3351	$793.32	$793.30	$793.40