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	$129.78	7.322%	$139.2825	$139.28	$139.30	$139.30
Purchase #2	$105.86	5.324%	$111.496	$111.50	$111.50	$111.50
Purchase #3	$116.35	5.317%	$122.5363	$122.54	$122.55	$122.50
Purchase #4	$178.86	9.519%	$195.8857	$195.89	$195.90	$195.90
Purchase #5	$30.47	4.208%	$31.7522	$31.75	$31.75	$31.80
Purchase #6	$207.48	10.364%	$228.9832	$228.98	$229.00	$229.00
Purchase #7	$18.41	3.762%	$19.1026	$19.10	$19.10	$19.10
7 purchase totals =	$787.21		$849.0385	$849.04	$849.10	$849.10