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	$78.27	5.796%	$82.8065	$82.81	$82.80	$82.80
Purchase #2	$55.44	6.296%	$58.9305	$58.93	$58.95	$58.90
Purchase #3	$116.36	3.568%	$120.5117	$120.51	$120.50	$120.50
Purchase #4	$40.61	13.222%	$45.9795	$45.98	$46.00	$46.00
Purchase #5	$50.53	7.555%	$54.3475	$54.35	$54.35	$54.30
Purchase #6	$81.86	4.744%	$85.7434	$85.74	$85.75	$85.70
Purchase #7	$58.32	5.767%	$61.6833	$61.68	$61.70	$61.70
7 purchase totals =	$481.39		$510.0024	$510.00	$510.05	$509.90