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	$163.61	11.288%	$182.0783	$182.08	$182.10	$182.10
Purchase #2	$81.30	11.447%	$90.6064	$90.61	$90.60	$90.60
Purchase #3	$159.75	9.152%	$174.3703	$174.37	$174.35	$174.40
Purchase #4	$79.79	10.679%	$88.3108	$88.31	$88.30	$88.30
Purchase #5	$174.75	5.425%	$184.2302	$184.23	$184.25	$184.20
Purchase #6	$73.62	11.141%	$81.822	$81.82	$81.80	$81.80
Purchase #7	$81.90	11.390%	$91.2284	$91.23	$91.25	$91.20
7 purchase totals =	$814.72		$892.6464	$892.65	$892.65	$892.60