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	$195.38	13.213%	$221.1956	$221.20	$221.20	$221.20
Purchase #2	$101.91	10.448%	$112.5576	$112.56	$112.55	$112.60
Purchase #3	$64.38	5.689%	$68.0426	$68.04	$68.05	$68.00
Purchase #4	$68.89	4.819%	$72.2098	$72.21	$72.20	$72.20
Purchase #5	$46.77	12.707%	$52.7131	$52.71	$52.70	$52.70
Purchase #6	$151.90	13.811%	$172.8789	$172.88	$172.90	$172.90
Purchase #7	$81.67	10.433%	$90.1906	$90.19	$90.20	$90.20
7 purchase totals =	$710.90		$789.7882	$789.79	$789.80	$789.80