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	$48.42	3.578%	$50.1525	$50.15	$50.15	$50.20
Purchase #2	$28.97	12.774%	$32.6706	$32.67	$32.65	$32.70
Purchase #3	$243.32	9.580%	$266.6301	$266.63	$266.65	$266.60
Purchase #4	$68.96	3.480%	$71.3598	$71.36	$71.35	$71.40
Purchase #5	$48.40	13.139%	$54.7593	$54.76	$54.75	$54.80
Purchase #6	$42.27	9.693%	$46.3672	$46.37	$46.35	$46.40
Purchase #7	$138.57	6.680%	$147.8265	$147.83	$147.85	$147.80
7 purchase totals =	$618.91		$669.7660	$669.77	$669.75	$669.90