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	$138.81	5.821%	$146.8901	$146.89	$146.90	$146.90
Purchase #2	$146.82	3.568%	$152.0585	$152.06	$152.05	$152.10
Purchase #3	$55.72	7.263%	$59.7669	$59.77	$59.75	$59.80
Purchase #4	$171.34	12.192%	$192.2298	$192.23	$192.25	$192.20
Purchase #5	$234.48	9.545%	$256.8611	$256.86	$256.85	$256.90
Purchase #6	$15.37	5.247%	$16.1765	$16.18	$16.20	$16.20
Purchase #7	$143.62	4.738%	$150.4247	$150.42	$150.40	$150.40
7 purchase totals =	$906.16		$974.4076	$974.41	$974.40	$974.50