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	$130.35	8.476%	$141.3985	$141.40	$141.40	$141.40
Purchase #2	$212.53	5.209%	$223.6007	$223.60	$223.60	$223.60
Purchase #3	$91.54	9.238%	$99.9965	$100.00	$100.00	$100.00
Purchase #4	$172.67	7.198%	$185.0988	$185.10	$185.10	$185.10
Purchase #5	$223.47	5.619%	$236.0268	$236.03	$236.05	$236.00
Purchase #6	$83.60	10.423%	$92.3136	$92.31	$92.30	$92.30
Purchase #7	$13.36	3.230%	$13.7915	$13.79	$13.80	$13.80
7 purchase totals =	$927.52		$992.2264	$992.23	$992.25	$992.20