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	$113.65	5.794%	$120.2349	$120.23	$120.25	$120.20
Purchase #2	$33.76	12.112%	$37.849	$37.85	$37.85	$37.80
Purchase #3	$41.40	3.337%	$42.7815	$42.78	$42.80	$42.80
Purchase #4	$78.72	9.195%	$85.9583	$85.96	$85.95	$86.00
Purchase #5	$238.44	5.184%	$250.8007	$250.80	$250.80	$250.80
Purchase #6	$109.79	6.188%	$116.5838	$116.58	$116.60	$116.60
Purchase #7	$97.51	4.517%	$101.9145	$101.91	$101.90	$101.90
7 purchase totals =	$713.27		$756.1227	$756.11	$756.15	$756.10