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	$9.61	4.670%	$10.0588	$10.06	$10.05	$10.10
Purchase #2	$61.99	9.505%	$67.8821	$67.88	$67.90	$67.90
Purchase #3	$105.46	4.291%	$109.9853	$109.99	$110.00	$110.00
Purchase #4	$80.54	3.234%	$83.1447	$83.14	$83.15	$83.10
Purchase #5	$222.64	13.854%	$253.4845	$253.48	$253.50	$253.50
Purchase #6	$92.75	13.684%	$105.4419	$105.44	$105.45	$105.40
Purchase #7	$101.96	11.310%	$113.4917	$113.49	$113.50	$113.50
7 purchase totals =	$674.95		$743.4890	$743.48	$743.55	$743.50