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	$28.72	3.837%	$29.822	$29.82	$29.80	$29.80
Purchase #2	$97.44	12.395%	$109.5177	$109.52	$109.50	$109.50
Purchase #3	$101.90	9.678%	$111.7619	$111.76	$111.75	$111.80
Purchase #4	$149.35	12.731%	$168.3637	$168.36	$168.35	$168.40
Purchase #5	$172.56	7.214%	$185.0085	$185.01	$185.00	$185.00
Purchase #6	$171.37	12.830%	$193.3568	$193.36	$193.35	$193.40
Purchase #7	$224.66	13.336%	$254.6207	$254.62	$254.60	$254.60
7 purchase totals =	$946.00		$1,052.4513	$1,052.45	$1,052.35	$1,052.50