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	$16.97	8.124%	$18.3486	$18.35	$18.35	$18.30
Purchase #2	$54.78	9.343%	$59.8981	$59.90	$59.90	$59.90
Purchase #3	$225.67	9.690%	$247.5374	$247.54	$247.55	$247.50
Purchase #4	$90.51	6.477%	$96.3723	$96.37	$96.35	$96.40
Purchase #5	$52.65	9.591%	$57.6997	$57.70	$57.70	$57.70
Purchase #6	$152.54	13.844%	$173.6576	$173.66	$173.65	$173.70
Purchase #7	$93.36	6.175%	$99.125	$99.13	$99.15	$99.10
7 purchase totals =	$686.48		$752.6387	$752.65	$752.65	$752.60