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	$154.61	11.320%	$172.1119	$172.11	$172.10	$172.10
Purchase #2	$245.94	11.420%	$274.0263	$274.03	$274.05	$274.00
Purchase #3	$34.69	13.503%	$39.3742	$39.37	$39.35	$39.40
Purchase #4	$82.77	8.364%	$89.6929	$89.69	$89.70	$89.70
Purchase #5	$88.88	7.648%	$95.6775	$95.68	$95.70	$95.70
Purchase #6	$150.75	11.630%	$168.2822	$168.28	$168.30	$168.30
Purchase #7	$61.29	9.814%	$67.305	$67.31	$67.30	$67.30
7 purchase totals =	$818.93		$906.4700	$906.47	$906.50	$906.50