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	$128.88	10.430%	$142.3222	$142.32	$142.30	$142.30
Purchase #2	$71.70	12.257%	$80.4883	$80.49	$80.50	$80.50
Purchase #3	$156.66	5.416%	$165.1447	$165.14	$165.15	$165.10
Purchase #4	$41.26	10.267%	$45.4962	$45.50	$45.50	$45.50
Purchase #5	$170.69	5.717%	$180.4483	$180.45	$180.45	$180.40
Purchase #6	$121.49	8.245%	$131.5069	$131.51	$131.50	$131.50
Purchase #7	$85.38	6.293%	$90.753	$90.75	$90.75	$90.80
7 purchase totals =	$776.06		$836.1596	$836.16	$836.15	$836.10