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	$211.54	12.254%	$237.4621	$237.46	$237.45	$237.50
Purchase #2	$85.84	5.393%	$90.4694	$90.47	$90.45	$90.50
Purchase #3	$109.59	11.579%	$122.2794	$122.28	$122.30	$122.30
Purchase #4	$67.34	9.723%	$73.8875	$73.89	$73.90	$73.90
Purchase #5	$37.54	8.655%	$40.7891	$40.79	$40.80	$40.80
Purchase #6	$202.28	3.834%	$210.0354	$210.04	$210.05	$210.00
Purchase #7	$113.34	8.682%	$123.1802	$123.18	$123.20	$123.20
7 purchase totals =	$827.47		$898.1031	$898.11	$898.15	$898.20