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	$60.79	11.555%	$67.8143	$67.81	$67.80	$67.80
Purchase #2	$79.35	6.211%	$84.2784	$84.28	$84.30	$84.30
Purchase #3	$10.75	9.425%	$11.7632	$11.76	$11.75	$11.80
Purchase #4	$56.82	5.449%	$59.9161	$59.92	$59.90	$59.90
Purchase #5	$30.50	5.145%	$32.0692	$32.07	$32.05	$32.10
Purchase #6	$48.67	6.632%	$51.8978	$51.90	$51.90	$51.90
Purchase #7	$6.83	7.847%	$7.366	$7.37	$7.35	$7.40
7 purchase totals =	$293.71		$315.1050	$315.11	$315.05	$315.20