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	$227.90	11.512%	$254.1358	$254.14	$254.15	$254.10
Purchase #2	$132.54	10.568%	$146.5468	$146.55	$146.55	$146.50
Purchase #3	$64.95	9.409%	$71.0611	$71.06	$71.05	$71.10
Purchase #4	$90.51	12.246%	$101.5939	$101.59	$101.60	$101.60
Purchase #5	$149.32	13.270%	$169.1348	$169.13	$169.15	$169.10
Purchase #6	$99.90	12.437%	$112.3246	$112.32	$112.30	$112.30
Purchase #7	$135.48	8.449%	$146.9267	$146.93	$146.95	$146.90
7 purchase totals =	$900.60		$1,001.7237	$1,001.72	$1,001.75	$1,001.60