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	$70.37	12.107%	$78.8897	$78.89	$78.90	$78.90
Purchase #2	$187.64	13.502%	$212.9752	$212.98	$213.00	$213.00
Purchase #3	$202.89	8.310%	$219.7502	$219.75	$219.75	$219.80
Purchase #4	$241.29	11.731%	$269.5957	$269.60	$269.60	$269.60
Purchase #5	$19.37	4.827%	$20.305	$20.31	$20.30	$20.30
Purchase #6	$148.32	8.445%	$160.8456	$160.85	$160.85	$160.80
Purchase #7	$200.45	13.847%	$228.2063	$228.21	$228.20	$228.20
7 purchase totals =	$1,070.33		$1,190.5677	$1,190.59	$1,190.60	$1,190.60