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	$125.32	9.148%	$136.7843	$136.78	$136.80	$136.80
Purchase #2	$176.39	6.753%	$188.3016	$188.30	$188.30	$188.30
Purchase #3	$179.56	9.386%	$196.4135	$196.41	$196.40	$196.40
Purchase #4	$214.75	5.753%	$227.1046	$227.10	$227.10	$227.10
Purchase #5	$30.66	11.732%	$34.257	$34.26	$34.25	$34.30
Purchase #6	$27.30	13.709%	$31.0426	$31.04	$31.05	$31.00
Purchase #7	$50.42	8.534%	$54.7228	$54.72	$54.70	$54.70
7 purchase totals =	$804.40		$868.6264	$868.61	$868.60	$868.60