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	$70.71	10.579%	$78.1904	$78.19	$78.20	$78.20
Purchase #2	$33.32	12.144%	$37.3664	$37.37	$37.35	$37.40
Purchase #3	$92.71	13.501%	$105.2268	$105.23	$105.25	$105.20
Purchase #4	$73.62	11.143%	$81.8235	$81.82	$81.80	$81.80
Purchase #5	$237.84	9.308%	$259.9781	$259.98	$260.00	$260.00
Purchase #6	$165.79	4.280%	$172.8858	$172.89	$172.90	$172.90
Purchase #7	$65.77	3.169%	$67.8543	$67.85	$67.85	$67.90
7 purchase totals =	$739.76		$803.3253	$803.33	$803.35	$803.40