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	$113.55	12.854%	$128.1457	$128.15	$128.15	$128.10
Purchase #2	$105.75	5.754%	$111.8349	$111.83	$111.85	$111.80
Purchase #3	$157.27	7.302%	$168.7539	$168.75	$168.75	$168.80
Purchase #4	$164.48	12.365%	$184.818	$184.82	$184.80	$184.80
Purchase #5	$42.91	13.641%	$48.7634	$48.76	$48.75	$48.80
Purchase #6	$188.51	3.362%	$194.8477	$194.85	$194.85	$194.80
Purchase #7	$22.93	13.245%	$25.9671	$25.97	$25.95	$26.00
7 purchase totals =	$795.40		$863.1307	$863.13	$863.10	$863.10