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	$249.97	5.835%	$264.5557	$264.56	$264.55	$264.60
Purchase #2	$155.84	10.548%	$172.278	$172.28	$172.30	$172.30
Purchase #3	$233.29	13.624%	$265.0734	$265.07	$265.05	$265.10
Purchase #4	$196.50	3.466%	$203.3107	$203.31	$203.30	$203.30
Purchase #5	$33.26	5.330%	$35.0328	$35.03	$35.05	$35.00
Purchase #6	$84.69	5.846%	$89.641	$89.64	$89.65	$89.60
Purchase #7	$51.30	4.843%	$53.7845	$53.78	$53.80	$53.80
7 purchase totals =	$1,004.85		$1,083.6761	$1,083.67	$1,083.70	$1,083.70