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	$33.98	9.581%	$37.2356	$37.24	$37.25	$37.20
Purchase #2	$98.27	6.813%	$104.9651	$104.97	$104.95	$105.00
Purchase #3	$135.58	8.355%	$146.9077	$146.91	$146.90	$146.90
Purchase #4	$86.62	4.760%	$90.7431	$90.74	$90.75	$90.70
Purchase #5	$43.92	5.862%	$46.4946	$46.49	$46.50	$46.50
Purchase #6	$51.47	5.419%	$54.2592	$54.26	$54.25	$54.30
Purchase #7	$81.77	6.123%	$86.7768	$86.78	$86.80	$86.80
7 purchase totals =	$531.61		$567.3821	$567.39	$567.40	$567.40