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	$37.56	5.566%	$39.6506	$39.65	$39.65	$39.70
Purchase #2	$180.40	11.178%	$200.5651	$200.57	$200.55	$200.60
Purchase #3	$231.33	9.501%	$253.3087	$253.31	$253.30	$253.30
Purchase #4	$208.57	9.584%	$228.5593	$228.56	$228.55	$228.60
Purchase #5	$154.28	7.782%	$166.2861	$166.29	$166.30	$166.30
Purchase #6	$101.29	10.664%	$112.0916	$112.09	$112.10	$112.10
Purchase #7	$37.58	9.864%	$41.2869	$41.29	$41.30	$41.30
7 purchase totals =	$951.01		$1,041.7483	$1,041.76	$1,041.75	$1,041.90