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	$34.59	8.147%	$37.408	$37.41	$37.40	$37.40
Purchase #2	$150.25	7.591%	$161.6555	$161.66	$161.65	$161.70
Purchase #3	$112.54	5.109%	$118.2897	$118.29	$118.30	$118.30
Purchase #4	$18.35	12.607%	$20.6634	$20.66	$20.65	$20.70
Purchase #5	$86.36	4.743%	$90.4561	$90.46	$90.45	$90.50
Purchase #6	$43.59	8.190%	$47.16	$47.16	$47.15	$47.20
Purchase #7	$197.87	13.162%	$223.9136	$223.91	$223.90	$223.90
7 purchase totals =	$643.55		$699.5463	$699.55	$699.50	$699.70