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	$89.31	3.624%	$92.5466	$92.55	$92.55	$92.50
Purchase #2	$119.72	5.496%	$126.2998	$126.30	$126.30	$126.30
Purchase #3	$71.92	3.642%	$74.5393	$74.54	$74.55	$74.50
Purchase #4	$52.43	5.716%	$55.4269	$55.43	$55.45	$55.40
Purchase #5	$18.37	10.576%	$20.3128	$20.31	$20.30	$20.30
Purchase #6	$187.27	5.862%	$198.2478	$198.25	$198.25	$198.20
Purchase #7	$138.86	4.333%	$144.8768	$144.88	$144.90	$144.90
7 purchase totals =	$677.88		$712.2500	$712.26	$712.30	$712.10