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	$9.40	8.231%	$10.1737	$10.17	$10.15	$10.20
Purchase #2	$94.91	13.386%	$107.6147	$107.61	$107.60	$107.60
Purchase #3	$197.78	8.766%	$215.1174	$215.12	$215.10	$215.10
Purchase #4	$130.99	10.420%	$144.6392	$144.64	$144.65	$144.60
Purchase #5	$223.59	8.844%	$243.3643	$243.36	$243.35	$243.40
Purchase #6	$31.40	3.586%	$32.526	$32.53	$32.55	$32.50
Purchase #7	$199.82	12.804%	$225.405	$225.41	$225.40	$225.40
7 purchase totals =	$887.89		$978.8403	$978.84	$978.80	$978.80