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	$85.78	7.742%	$92.4211	$92.42	$92.40	$92.40
Purchase #2	$241.89	6.109%	$256.6671	$256.67	$256.65	$256.70
Purchase #3	$123.54	3.801%	$128.2358	$128.24	$128.25	$128.20
Purchase #4	$168.48	10.139%	$185.5622	$185.56	$185.55	$185.60
Purchase #5	$20.35	12.614%	$22.9169	$22.92	$22.90	$22.90
Purchase #6	$56.78	3.169%	$58.5794	$58.58	$58.60	$58.60
Purchase #7	$23.76	13.376%	$26.9381	$26.94	$26.95	$26.90
7 purchase totals =	$720.58		$771.3206	$771.33	$771.30	$771.30