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	$166.55	3.317%	$172.0745	$172.07	$172.05	$172.10
Purchase #2	$28.35	8.294%	$30.7013	$30.70	$30.70	$30.70
Purchase #3	$250.77	12.141%	$281.216	$281.22	$281.20	$281.20
Purchase #4	$62.79	13.221%	$71.0915	$71.09	$71.10	$71.10
Purchase #5	$130.47	7.317%	$140.0165	$140.02	$140.00	$140.00
Purchase #6	$90.41	11.627%	$100.922	$100.92	$100.90	$100.90
Purchase #7	$73.49	6.717%	$78.4263	$78.43	$78.45	$78.40
7 purchase totals =	$802.83		$874.4481	$874.45	$874.40	$874.40