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	$247.36	12.824%	$279.0814	$279.08	$279.10	$279.10
Purchase #2	$68.61	9.330%	$75.0113	$75.01	$75.00	$75.00
Purchase #3	$172.26	9.361%	$188.3853	$188.39	$188.40	$188.40
Purchase #4	$13.52	3.112%	$13.9407	$13.94	$13.95	$13.90
Purchase #5	$200.89	9.449%	$219.8721	$219.87	$219.85	$219.90
Purchase #6	$144.25	5.258%	$151.8347	$151.83	$151.85	$151.80
Purchase #7	$78.63	12.753%	$88.6577	$88.66	$88.65	$88.70
7 purchase totals =	$925.52		$1,016.7832	$1,016.78	$1,016.80	$1,016.80