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	$90.30	4.778%	$94.6145	$94.61	$94.60	$94.60
Purchase #2	$98.96	10.813%	$109.6605	$109.66	$109.65	$109.70
Purchase #3	$50.29	9.484%	$55.0595	$55.06	$55.05	$55.10
Purchase #4	$165.30	4.729%	$173.117	$173.12	$173.10	$173.10
Purchase #5	$111.33	3.731%	$115.4837	$115.48	$115.50	$115.50
Purchase #6	$136.60	10.668%	$151.1725	$151.17	$151.15	$151.20
Purchase #7	$149.96	6.616%	$159.8814	$159.88	$159.90	$159.90
7 purchase totals =	$802.74		$858.9891	$858.98	$858.95	$859.10