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	$35.98	5.568%	$37.9834	$37.98	$38.00	$38.00
Purchase #2	$94.67	9.552%	$103.7129	$103.71	$103.70	$103.70
Purchase #3	$93.35	13.731%	$106.1679	$106.17	$106.15	$106.20
Purchase #4	$34.82	9.844%	$38.2477	$38.25	$38.25	$38.20
Purchase #5	$237.28	11.648%	$264.9184	$264.92	$264.90	$264.90
Purchase #6	$78.89	4.173%	$82.1821	$82.18	$82.20	$82.20
Purchase #7	$197.78	4.188%	$206.063	$206.06	$206.05	$206.10
7 purchase totals =	$772.77		$839.2754	$839.27	$839.25	$839.30