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	$10.55	5.273%	$11.1063	$11.11	$11.10	$11.10
Purchase #2	$25.91	7.444%	$27.8387	$27.84	$27.85	$27.80
Purchase #3	$46.96	8.453%	$50.9295	$50.93	$50.95	$50.90
Purchase #4	$100.40	11.267%	$111.7121	$111.71	$111.70	$111.70
Purchase #5	$125.33	4.689%	$131.2067	$131.21	$131.20	$131.20
Purchase #6	$120.83	13.598%	$137.2605	$137.26	$137.25	$137.30
Purchase #7	$112.53	6.467%	$119.8073	$119.81	$119.80	$119.80
7 purchase totals =	$542.51		$589.8611	$589.87	$589.85	$589.80