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	$130.89	4.337%	$136.5667	$136.57	$136.55	$136.60
Purchase #2	$146.27	6.747%	$156.1388	$156.14	$156.15	$156.10
Purchase #3	$77.52	11.746%	$86.6255	$86.63	$86.65	$86.60
Purchase #4	$153.64	13.317%	$174.1002	$174.10	$174.10	$174.10
Purchase #5	$41.40	3.728%	$42.9434	$42.94	$42.95	$42.90
Purchase #6	$86.59	9.610%	$94.9113	$94.91	$94.90	$94.90
Purchase #7	$17.33	8.662%	$18.8311	$18.83	$18.85	$18.80
7 purchase totals =	$653.64		$710.1170	$710.12	$710.15	$710.00