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	$120.95	3.865%	$125.6247	$125.62	$125.60	$125.60
Purchase #2	$134.81	11.650%	$150.5154	$150.52	$150.50	$150.50
Purchase #3	$240.89	5.339%	$253.7511	$253.75	$253.75	$253.80
Purchase #4	$60.50	4.610%	$63.2891	$63.29	$63.30	$63.30
Purchase #5	$105.32	11.543%	$117.4771	$117.48	$117.50	$117.50
Purchase #6	$17.61	10.344%	$19.4316	$19.43	$19.45	$19.40
Purchase #7	$63.48	12.308%	$71.2931	$71.29	$71.30	$71.30
7 purchase totals =	$743.56		$801.3821	$801.38	$801.40	$801.40