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	$117.49	9.111%	$128.1945	$128.19	$128.20	$128.20
Purchase #2	$75.31	10.203%	$82.9939	$82.99	$83.00	$83.00
Purchase #3	$202.28	10.658%	$223.839	$223.84	$223.85	$223.80
Purchase #4	$94.78	11.257%	$105.4494	$105.45	$105.45	$105.40
Purchase #5	$70.51	11.224%	$78.424	$78.42	$78.40	$78.40
Purchase #6	$184.61	7.325%	$198.1327	$198.13	$198.15	$198.10
Purchase #7	$73.35	11.475%	$81.7669	$81.77	$81.75	$81.80
7 purchase totals =	$818.33		$898.8004	$898.79	$898.80	$898.70