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	$166.39	12.584%	$187.3285	$187.33	$187.35	$187.30
Purchase #2	$244.33	10.573%	$270.163	$270.16	$270.15	$270.20
Purchase #3	$66.57	9.485%	$72.8842	$72.88	$72.90	$72.90
Purchase #4	$215.38	13.586%	$244.6415	$244.64	$244.65	$244.60
Purchase #5	$73.72	8.422%	$79.9287	$79.93	$79.95	$79.90
Purchase #6	$82.66	3.583%	$85.6217	$85.62	$85.60	$85.60
Purchase #7	$83.70	11.374%	$93.22	$93.22	$93.20	$93.20
7 purchase totals =	$932.75		$1,033.7876	$1,033.78	$1,033.80	$1,033.70