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	$33.88	9.707%	$37.1687	$37.17	$37.15	$37.20
Purchase #2	$11.50	12.656%	$12.9554	$12.96	$12.95	$13.00
Purchase #3	$219.77	5.372%	$231.576	$231.58	$231.60	$231.60
Purchase #4	$190.69	6.858%	$203.7675	$203.77	$203.75	$203.80
Purchase #5	$53.82	11.144%	$59.8177	$59.82	$59.80	$59.80
Purchase #6	$65.72	8.272%	$71.1564	$71.16	$71.15	$71.20
Purchase #7	$155.48	11.391%	$173.1907	$173.19	$173.20	$173.20
7 purchase totals =	$730.86		$789.6324	$789.65	$789.60	$789.80