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	$30.69	3.422%	$31.7402	$31.74	$31.75	$31.70
Purchase #2	$16.78	13.709%	$19.0804	$19.08	$19.10	$19.10
Purchase #3	$55.29	11.352%	$61.5665	$61.57	$61.55	$61.60
Purchase #4	$151.40	5.562%	$159.8209	$159.82	$159.80	$159.80
Purchase #5	$47.96	8.768%	$52.1651	$52.17	$52.15	$52.20
Purchase #6	$37.41	9.150%	$40.833	$40.83	$40.85	$40.80
Purchase #7	$123.91	13.805%	$141.0158	$141.02	$141.00	$141.00
7 purchase totals =	$463.44		$506.2219	$506.23	$506.20	$506.20