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	$198.77	12.420%	$223.4572	$223.46	$223.45	$223.50
Purchase #2	$93.57	4.329%	$97.6206	$97.62	$97.60	$97.60
Purchase #3	$91.39	8.557%	$99.2102	$99.21	$99.20	$99.20
Purchase #4	$34.41	9.383%	$37.6387	$37.64	$37.65	$37.60
Purchase #5	$237.34	10.420%	$262.0708	$262.07	$262.05	$262.10
Purchase #6	$81.43	13.785%	$92.6551	$92.66	$92.65	$92.70
Purchase #7	$97.44	8.424%	$105.6483	$105.65	$105.65	$105.60
7 purchase totals =	$834.35		$918.3009	$918.31	$918.25	$918.30