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	$11.53	3.492%	$11.9326	$11.93	$11.95	$11.90
Purchase #2	$90.42	12.866%	$102.0534	$102.05	$102.05	$102.10
Purchase #3	$238.29	6.339%	$253.3952	$253.40	$253.40	$253.40
Purchase #4	$104.73	6.335%	$111.3646	$111.36	$111.35	$111.40
Purchase #5	$116.60	11.243%	$129.7093	$129.71	$129.70	$129.70
Purchase #6	$188.38	4.187%	$196.2675	$196.27	$196.25	$196.30
Purchase #7	$31.40	5.423%	$33.1028	$33.10	$33.10	$33.10
7 purchase totals =	$781.35		$837.8254	$837.82	$837.80	$837.90