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	$203.46	12.867%	$229.6392	$229.64	$229.65	$229.60
Purchase #2	$175.56	8.871%	$191.1339	$191.13	$191.15	$191.10
Purchase #3	$151.51	7.374%	$162.6823	$162.68	$162.70	$162.70
Purchase #4	$238.46	12.560%	$268.4106	$268.41	$268.40	$268.40
Purchase #5	$210.74	3.369%	$217.8398	$217.84	$217.85	$217.80
Purchase #6	$33.76	11.563%	$37.6637	$37.66	$37.65	$37.70
Purchase #7	$170.85	11.754%	$190.9317	$190.93	$190.95	$190.90
7 purchase totals =	$1,184.34		$1,298.3012	$1,298.29	$1,298.35	$1,298.20