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	$187.43	12.168%	$210.2365	$210.24	$210.25	$210.20
Purchase #2	$37.84	6.160%	$40.1709	$40.17	$40.15	$40.20
Purchase #3	$53.54	10.629%	$59.2308	$59.23	$59.25	$59.20
Purchase #4	$10.51	3.462%	$10.8739	$10.87	$10.85	$10.90
Purchase #5	$25.51	12.681%	$28.7449	$28.74	$28.75	$28.70
Purchase #6	$162.88	4.829%	$170.7455	$170.75	$170.75	$170.70
Purchase #7	$92.60	3.130%	$95.4984	$95.50	$95.50	$95.50
7 purchase totals =	$570.31		$615.5009	$615.50	$615.50	$615.40