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	$70.47	11.308%	$78.4387	$78.44	$78.45	$78.40
Purchase #2	$131.79	13.735%	$149.8914	$149.89	$149.90	$149.90
Purchase #3	$58.40	9.404%	$63.8919	$63.89	$63.90	$63.90
Purchase #4	$49.99	8.243%	$54.1107	$54.11	$54.10	$54.10
Purchase #5	$81.59	10.480%	$90.1406	$90.14	$90.15	$90.10
Purchase #6	$139.85	5.522%	$147.5725	$147.57	$147.55	$147.60
Purchase #7	$212.97	9.474%	$233.1468	$233.15	$233.15	$233.10
7 purchase totals =	$745.06		$817.1926	$817.19	$817.20	$817.10