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	$76.59	9.520%	$83.8814	$83.88	$83.90	$83.90
Purchase #2	$40.87	11.701%	$45.6522	$45.65	$45.65	$45.70
Purchase #3	$211.68	13.251%	$239.7297	$239.73	$239.75	$239.70
Purchase #4	$180.69	11.432%	$201.3465	$201.35	$201.35	$201.30
Purchase #5	$86.85	4.653%	$90.8911	$90.89	$90.90	$90.90
Purchase #6	$119.73	3.198%	$123.559	$123.56	$123.55	$123.60
Purchase #7	$13.25	9.246%	$14.4751	$14.48	$14.50	$14.50
7 purchase totals =	$729.66		$799.5350	$799.54	$799.60	$799.60