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	$138.93	6.693%	$148.2286	$148.23	$148.25	$148.20
Purchase #2	$98.35	13.421%	$111.5496	$111.55	$111.55	$111.50
Purchase #3	$123.78	9.836%	$135.955	$135.96	$135.95	$136.00
Purchase #4	$31.76	11.482%	$35.4067	$35.41	$35.40	$35.40
Purchase #5	$89.69	9.735%	$98.4213	$98.42	$98.40	$98.40
Purchase #6	$34.41	4.186%	$35.8504	$35.85	$35.85	$35.90
Purchase #7	$80.48	10.804%	$89.1751	$89.18	$89.20	$89.20
7 purchase totals =	$597.40		$654.5867	$654.60	$654.60	$654.60