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	$94.56	11.490%	$105.4249	$105.42	$105.40	$105.40
Purchase #2	$203.94	9.780%	$223.8853	$223.89	$223.90	$223.90
Purchase #3	$135.71	7.834%	$146.3415	$146.34	$146.35	$146.30
Purchase #4	$147.56	9.845%	$162.0873	$162.09	$162.10	$162.10
Purchase #5	$218.68	4.278%	$228.0351	$228.04	$228.05	$228.00
Purchase #6	$81.72	8.224%	$88.4407	$88.44	$88.45	$88.40
Purchase #7	$107.79	7.685%	$116.0737	$116.07	$116.05	$116.10
7 purchase totals =	$989.96		$1,070.2885	$1,070.29	$1,070.30	$1,070.20