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	$47.96	4.686%	$50.2074	$50.21	$50.20	$50.20
Purchase #2	$219.91	4.639%	$230.1116	$230.11	$230.10	$230.10
Purchase #3	$190.66	4.246%	$198.7554	$198.76	$198.75	$198.80
Purchase #4	$83.99	6.187%	$89.1865	$89.19	$89.20	$89.20
Purchase #5	$108.86	8.663%	$118.2905	$118.29	$118.30	$118.30
Purchase #6	$6.78	4.584%	$7.0908	$7.09	$7.10	$7.10
Purchase #7	$57.45	3.797%	$59.6314	$59.63	$59.65	$59.60
7 purchase totals =	$715.61		$753.2736	$753.28	$753.30	$753.30