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	$184.63	4.218%	$192.4177	$192.42	$192.40	$192.40
Purchase #2	$158.40	6.654%	$168.9399	$168.94	$168.95	$168.90
Purchase #3	$116.80	11.583%	$130.3289	$130.33	$130.35	$130.30
Purchase #4	$90.27	10.820%	$100.0372	$100.04	$100.05	$100.00
Purchase #5	$209.33	3.510%	$216.6775	$216.68	$216.70	$216.70
Purchase #6	$172.39	8.846%	$187.6396	$187.64	$187.65	$187.60
Purchase #7	$218.30	7.315%	$234.2686	$234.27	$234.25	$234.30
7 purchase totals =	$1,150.12		$1,230.3094	$1,230.32	$1,230.35	$1,230.20