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	$38.94	3.240%	$40.2017	$40.20	$40.20	$40.20
Purchase #2	$39.49	7.539%	$42.4672	$42.47	$42.45	$42.50
Purchase #3	$159.62	7.499%	$171.5899	$171.59	$171.60	$171.60
Purchase #4	$80.59	5.841%	$85.2973	$85.30	$85.30	$85.30
Purchase #5	$89.47	11.405%	$99.6741	$99.67	$99.65	$99.70
Purchase #6	$79.29	6.125%	$84.1465	$84.15	$84.15	$84.10
Purchase #7	$105.40	6.522%	$112.2742	$112.27	$112.25	$112.30
7 purchase totals =	$592.80		$635.6509	$635.65	$635.60	$635.70