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	$249.69	10.465%	$275.8201	$275.82	$275.80	$275.80
Purchase #2	$125.58	13.729%	$142.8209	$142.82	$142.80	$142.80
Purchase #3	$17.96	12.685%	$20.2382	$20.24	$20.25	$20.20
Purchase #4	$67.30	3.269%	$69.5	$69.50	$69.50	$69.50
Purchase #5	$242.48	5.675%	$256.2407	$256.24	$256.25	$256.20
Purchase #6	$7.33	9.117%	$7.9983	$8.00	$8.00	$8.00
Purchase #7	$161.45	6.855%	$172.5174	$172.52	$172.50	$172.50
7 purchase totals =	$871.79		$945.1356	$945.14	$945.10	$945.00