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	$26.29	9.734%	$28.8491	$28.85	$28.85	$28.80
Purchase #2	$70.74	13.530%	$80.3111	$80.31	$80.30	$80.30
Purchase #3	$246.77	4.532%	$257.9536	$257.95	$257.95	$258.00
Purchase #4	$71.77	9.851%	$78.8401	$78.84	$78.85	$78.80
Purchase #5	$46.89	7.385%	$50.3528	$50.35	$50.35	$50.40
Purchase #6	$161.88	3.366%	$167.3289	$167.33	$167.35	$167.30
Purchase #7	$139.91	7.510%	$150.4172	$150.42	$150.40	$150.40
7 purchase totals =	$764.25		$814.0528	$814.05	$814.05	$814.00