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	$81.28	12.538%	$91.4709	$91.47	$91.45	$91.50
Purchase #2	$32.29	9.165%	$35.2494	$35.25	$35.25	$35.20
Purchase #3	$218.59	10.427%	$241.3824	$241.38	$241.40	$241.40
Purchase #4	$96.42	10.564%	$106.6058	$106.61	$106.60	$106.60
Purchase #5	$6.79	10.191%	$7.482	$7.48	$7.50	$7.50
Purchase #6	$100.90	3.462%	$104.3932	$104.39	$104.40	$104.40
Purchase #7	$137.96	12.426%	$155.1029	$155.10	$155.10	$155.10
7 purchase totals =	$674.23		$741.6866	$741.68	$741.70	$741.70