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	$246.62	13.238%	$279.2676	$279.27	$279.25	$279.30
Purchase #2	$16.61	11.819%	$18.5731	$18.57	$18.55	$18.60
Purchase #3	$160.40	13.627%	$182.2577	$182.26	$182.25	$182.30
Purchase #4	$115.82	10.435%	$127.9058	$127.91	$127.90	$127.90
Purchase #5	$159.86	6.554%	$170.3372	$170.34	$170.35	$170.30
Purchase #6	$110.50	7.607%	$118.9057	$118.91	$118.90	$118.90
Purchase #7	$47.25	6.208%	$50.1833	$50.18	$50.20	$50.20
7 purchase totals =	$857.06		$947.4304	$947.44	$947.40	$947.50