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	$173.98	13.177%	$196.9053	$196.91	$196.90	$196.90
Purchase #2	$225.30	12.437%	$253.3206	$253.32	$253.30	$253.30
Purchase #3	$199.39	13.173%	$225.6556	$225.66	$225.65	$225.70
Purchase #4	$57.93	13.743%	$65.8913	$65.89	$65.90	$65.90
Purchase #5	$162.89	11.486%	$181.5995	$181.60	$181.60	$181.60
Purchase #6	$155.37	9.139%	$169.5693	$169.57	$169.55	$169.60
Purchase #7	$123.64	4.617%	$129.3485	$129.35	$129.35	$129.30
7 purchase totals =	$1,098.50		$1,222.2901	$1,222.30	$1,222.25	$1,222.30