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	$9.78	6.366%	$10.4026	$10.40	$10.40	$10.40
Purchase #2	$167.80	12.331%	$188.4914	$188.49	$188.50	$188.50
Purchase #3	$132.82	13.423%	$150.6484	$150.65	$150.65	$150.60
Purchase #4	$81.26	13.869%	$92.5299	$92.53	$92.55	$92.50
Purchase #5	$55.92	3.330%	$57.7821	$57.78	$57.80	$57.80
Purchase #6	$78.82	8.619%	$85.6135	$85.61	$85.60	$85.60
Purchase #7	$143.79	9.288%	$157.1452	$157.15	$157.15	$157.10
7 purchase totals =	$670.19		$742.6131	$742.61	$742.65	$742.50