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	$189.39	5.796%	$200.367	$200.37	$200.35	$200.40
Purchase #2	$45.86	12.697%	$51.6828	$51.68	$51.70	$51.70
Purchase #3	$97.56	7.680%	$105.0526	$105.05	$105.05	$105.10
Purchase #4	$242.48	4.819%	$254.1651	$254.17	$254.15	$254.20
Purchase #5	$152.62	11.178%	$169.6799	$169.68	$169.70	$169.70
Purchase #6	$36.54	12.604%	$41.1455	$41.15	$41.15	$41.10
Purchase #7	$12.38	7.601%	$13.321	$13.32	$13.30	$13.30
7 purchase totals =	$776.83		$835.4139	$835.42	$835.40	$835.50