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	$54.41	8.465%	$59.0158	$59.02	$59.00	$59.00
Purchase #2	$249.61	11.371%	$277.9932	$277.99	$278.00	$278.00
Purchase #3	$169.49	9.260%	$185.1848	$185.18	$185.20	$185.20
Purchase #4	$116.70	11.806%	$130.4776	$130.48	$130.50	$130.50
Purchase #5	$78.69	12.237%	$88.3193	$88.32	$88.30	$88.30
Purchase #6	$51.47	9.511%	$56.3653	$56.37	$56.35	$56.40
Purchase #7	$125.79	12.628%	$141.6748	$141.67	$141.65	$141.70
7 purchase totals =	$846.16		$939.0308	$939.03	$939.00	$939.10