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	$224.27	4.156%	$233.5907	$233.59	$233.60	$233.60
Purchase #2	$107.52	7.191%	$115.2518	$115.25	$115.25	$115.30
Purchase #3	$223.50	8.857%	$243.2954	$243.30	$243.30	$243.30
Purchase #4	$69.96	12.258%	$78.5357	$78.54	$78.55	$78.50
Purchase #5	$206.53	3.686%	$214.1427	$214.14	$214.15	$214.10
Purchase #6	$5.36	11.107%	$5.9553	$5.96	$5.95	$6.00
Purchase #7	$79.25	13.419%	$89.8846	$89.88	$89.90	$89.90
7 purchase totals =	$916.39		$980.6562	$980.66	$980.70	$980.70