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	$34.41	6.682%	$36.7093	$36.71	$36.70	$36.70
Purchase #2	$6.59	10.496%	$7.2817	$7.28	$7.30	$7.30
Purchase #3	$37.71	7.574%	$40.5662	$40.57	$40.55	$40.60
Purchase #4	$112.34	4.504%	$117.3998	$117.40	$117.40	$117.40
Purchase #5	$117.44	12.232%	$131.8053	$131.81	$131.80	$131.80
Purchase #6	$243.59	11.519%	$271.6491	$271.65	$271.65	$271.60
Purchase #7	$40.68	12.693%	$45.8435	$45.84	$45.85	$45.80
7 purchase totals =	$592.76		$651.2549	$651.26	$651.25	$651.20