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	$130.33	9.420%	$142.6071	$142.61	$142.60	$142.60
Purchase #2	$87.27	11.293%	$97.1254	$97.13	$97.15	$97.10
Purchase #3	$133.63	12.684%	$150.5796	$150.58	$150.60	$150.60
Purchase #4	$202.66	10.118%	$223.1651	$223.17	$223.15	$223.20
Purchase #5	$53.61	13.501%	$60.8479	$60.85	$60.85	$60.80
Purchase #6	$48.40	9.873%	$53.1785	$53.18	$53.20	$53.20
Purchase #7	$76.56	13.144%	$86.623	$86.62	$86.60	$86.60
7 purchase totals =	$732.46		$814.1266	$814.14	$814.15	$814.10