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	$70.66	10.719%	$78.234	$78.23	$78.25	$78.20
Purchase #2	$113.51	12.424%	$127.6125	$127.61	$127.60	$127.60
Purchase #3	$82.57	10.858%	$91.5355	$91.54	$91.55	$91.50
Purchase #4	$205.27	11.337%	$228.5415	$228.54	$228.55	$228.50
Purchase #5	$157.86	13.450%	$179.0922	$179.09	$179.10	$179.10
Purchase #6	$52.62	11.759%	$58.8076	$58.81	$58.80	$58.80
Purchase #7	$148.79	7.357%	$159.7365	$159.74	$159.75	$159.70
7 purchase totals =	$831.28		$923.5598	$923.56	$923.60	$923.40