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	$39.95	13.485%	$45.3373	$45.34	$45.35	$45.30
Purchase #2	$43.54	11.150%	$48.3947	$48.39	$48.40	$48.40
Purchase #3	$196.83	7.827%	$212.2359	$212.24	$212.25	$212.20
Purchase #4	$224.99	6.157%	$238.8426	$238.84	$238.85	$238.80
Purchase #5	$229.52	11.225%	$255.2836	$255.28	$255.30	$255.30
Purchase #6	$229.80	9.170%	$250.8727	$250.87	$250.85	$250.90
Purchase #7	$245.26	3.489%	$253.8171	$253.82	$253.80	$253.80
7 purchase totals =	$1,209.89		$1,304.7839	$1,304.78	$1,304.80	$1,304.70