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	$172.47	6.711%	$184.0445	$184.04	$184.05	$184.00
Purchase #2	$132.36	11.529%	$147.6198	$147.62	$147.60	$147.60
Purchase #3	$130.42	12.188%	$146.3156	$146.32	$146.30	$146.30
Purchase #4	$157.99	13.862%	$179.8906	$179.89	$179.90	$179.90
Purchase #5	$71.94	11.803%	$80.4311	$80.43	$80.45	$80.40
Purchase #6	$14.32	10.148%	$15.7732	$15.77	$15.75	$15.80
Purchase #7	$115.76	13.309%	$131.1665	$131.17	$131.15	$131.20
7 purchase totals =	$795.26		$885.2413	$885.24	$885.20	$885.20