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	$181.59	9.811%	$199.4058	$199.41	$199.40	$199.40
Purchase #2	$215.93	12.180%	$242.2303	$242.23	$242.25	$242.20
Purchase #3	$214.40	11.150%	$238.3056	$238.31	$238.30	$238.30
Purchase #4	$69.36	12.703%	$78.1708	$78.17	$78.15	$78.20
Purchase #5	$163.28	6.551%	$173.9765	$173.98	$174.00	$174.00
Purchase #6	$135.78	11.589%	$151.5155	$151.52	$151.50	$151.50
Purchase #7	$105.31	10.517%	$116.3855	$116.39	$116.40	$116.40
7 purchase totals =	$1,085.65		$1,199.9900	$1,200.01	$1,200.00	$1,200.00