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	$63.31	5.149%	$66.5698	$66.57	$66.55	$66.60
Purchase #2	$33.46	13.283%	$37.9045	$37.90	$37.90	$37.90
Purchase #3	$39.95	5.281%	$42.0598	$42.06	$42.05	$42.10
Purchase #4	$123.97	5.322%	$130.5677	$130.57	$130.55	$130.60
Purchase #5	$53.32	10.586%	$58.9645	$58.96	$58.95	$59.00
Purchase #6	$40.70	4.206%	$42.4118	$42.41	$42.40	$42.40
Purchase #7	$94.80	6.851%	$101.2947	$101.29	$101.30	$101.30
7 purchase totals =	$449.51		$479.7728	$479.76	$479.70	$479.90