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	$39.51	8.102%	$42.7111	$42.71	$42.70	$42.70
Purchase #2	$39.69	11.140%	$44.1115	$44.11	$44.10	$44.10
Purchase #3	$41.98	8.447%	$45.5261	$45.53	$45.55	$45.50
Purchase #4	$13.40	5.736%	$14.1686	$14.17	$14.15	$14.20
Purchase #5	$69.34	9.831%	$76.1568	$76.16	$76.15	$76.20
Purchase #6	$105.51	10.667%	$116.7648	$116.76	$116.75	$116.80
Purchase #7	$169.51	9.501%	$185.6151	$185.62	$185.60	$185.60
7 purchase totals =	$478.94		$525.0540	$525.06	$525.00	$525.10