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	$100.71	4.735%	$105.4786	$105.48	$105.50	$105.50
Purchase #2	$165.55	11.802%	$185.0882	$185.09	$185.10	$185.10
Purchase #3	$100.92	12.662%	$113.6985	$113.70	$113.70	$113.70
Purchase #4	$223.49	12.660%	$251.7838	$251.78	$251.80	$251.80
Purchase #5	$57.29	8.529%	$62.1763	$62.18	$62.20	$62.20
Purchase #6	$90.81	8.444%	$98.478	$98.48	$98.50	$98.50
Purchase #7	$170.59	8.797%	$185.5968	$185.60	$185.60	$185.60
7 purchase totals =	$909.36		$1,002.3002	$1,002.31	$1,002.40	$1,002.40