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	$75.87	5.250%	$79.8532	$79.85	$79.85	$79.90
Purchase #2	$105.81	11.186%	$117.6459	$117.65	$117.65	$117.60
Purchase #3	$162.87	6.573%	$173.5754	$173.58	$173.60	$173.60
Purchase #4	$79.30	12.650%	$89.3315	$89.33	$89.35	$89.30
Purchase #5	$56.30	10.821%	$62.3922	$62.39	$62.40	$62.40
Purchase #6	$239.98	10.112%	$264.2468	$264.25	$264.25	$264.20
Purchase #7	$94.34	5.564%	$99.5891	$99.59	$99.60	$99.60
7 purchase totals =	$814.47		$886.6341	$886.64	$886.70	$886.60