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	$25.60	9.586%	$28.054	$28.05	$28.05	$28.10
Purchase #2	$73.90	6.393%	$78.6244	$78.62	$78.60	$78.60
Purchase #3	$10.58	12.138%	$11.8642	$11.86	$11.85	$11.90
Purchase #4	$120.73	3.657%	$125.1451	$125.15	$125.15	$125.10
Purchase #5	$36.67	6.684%	$39.121	$39.12	$39.10	$39.10
Purchase #6	$77.30	4.127%	$80.4902	$80.49	$80.50	$80.50
Purchase #7	$211.39	5.211%	$222.4055	$222.41	$222.40	$222.40
7 purchase totals =	$556.17		$585.7044	$585.70	$585.65	$585.70