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	$37.62	6.554%	$40.0856	$40.09	$40.10	$40.10
Purchase #2	$86.50	6.543%	$92.1597	$92.16	$92.15	$92.20
Purchase #3	$67.45	4.331%	$70.3713	$70.37	$70.35	$70.40
Purchase #4	$222.42	10.112%	$244.9111	$244.91	$244.90	$244.90
Purchase #5	$42.34	12.140%	$47.4801	$47.48	$47.50	$47.50
Purchase #6	$130.85	6.763%	$139.6994	$139.70	$139.70	$139.70
Purchase #7	$51.54	6.747%	$55.0174	$55.02	$55.00	$55.00
7 purchase totals =	$638.72		$689.7246	$689.73	$689.70	$689.80