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	$35.44	5.855%	$37.515	$37.52	$37.50	$37.50
Purchase #2	$244.60	12.625%	$275.4808	$275.48	$275.50	$275.50
Purchase #3	$98.79	5.529%	$104.2521	$104.25	$104.25	$104.30
Purchase #4	$26.99	9.154%	$29.4607	$29.46	$29.45	$29.50
Purchase #5	$40.58	11.812%	$45.3733	$45.37	$45.35	$45.40
Purchase #6	$36.52	5.310%	$38.4592	$38.46	$38.45	$38.50
Purchase #7	$6.80	10.394%	$7.5068	$7.51	$7.50	$7.50
7 purchase totals =	$489.72		$538.0479	$538.05	$538.00	$538.20