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	$126.66	6.356%	$134.7105	$134.71	$134.70	$134.70
Purchase #2	$193.45	11.263%	$215.2383	$215.24	$215.25	$215.20
Purchase #3	$93.89	12.319%	$105.4563	$105.46	$105.45	$105.50
Purchase #4	$40.55	3.735%	$42.0645	$42.06	$42.05	$42.10
Purchase #5	$129.45	11.874%	$144.8209	$144.82	$144.80	$144.80
Purchase #6	$244.79	5.587%	$258.4664	$258.47	$258.45	$258.50
Purchase #7	$50.35	7.312%	$54.0316	$54.03	$54.05	$54.00
7 purchase totals =	$879.14		$954.7885	$954.79	$954.75	$954.80