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	$104.98	6.206%	$111.4951	$111.50	$111.50	$111.50
Purchase #2	$221.29	4.394%	$231.0135	$231.01	$231.00	$231.00
Purchase #3	$56.34	5.127%	$59.2286	$59.23	$59.25	$59.20
Purchase #4	$166.75	5.374%	$175.7111	$175.71	$175.70	$175.70
Purchase #5	$220.38	10.547%	$243.6235	$243.62	$243.60	$243.60
Purchase #6	$242.50	3.412%	$250.7741	$250.77	$250.75	$250.80
Purchase #7	$90.28	4.792%	$94.6062	$94.61	$94.60	$94.60
7 purchase totals =	$1,102.52		$1,166.4521	$1,166.45	$1,166.40	$1,166.40