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	$243.30	8.679%	$264.416	$264.42	$264.40	$264.40
Purchase #2	$14.59	6.108%	$15.4812	$15.48	$15.50	$15.50
Purchase #3	$152.70	9.268%	$166.8522	$166.85	$166.85	$166.90
Purchase #4	$61.34	5.816%	$64.9075	$64.91	$64.90	$64.90
Purchase #5	$174.34	6.355%	$185.4193	$185.42	$185.40	$185.40
Purchase #6	$84.75	7.223%	$90.8715	$90.87	$90.85	$90.90
Purchase #7	$122.32	8.493%	$132.7086	$132.71	$132.70	$132.70
7 purchase totals =	$853.34		$920.6563	$920.66	$920.60	$920.70