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	$37.54	8.670%	$40.7947	$40.79	$40.80	$40.80
Purchase #2	$175.65	7.272%	$188.4233	$188.42	$188.40	$188.40
Purchase #3	$47.27	4.662%	$49.4737	$49.47	$49.45	$49.50
Purchase #4	$171.77	13.840%	$195.543	$195.54	$195.55	$195.50
Purchase #5	$164.45	12.135%	$184.406	$184.41	$184.40	$184.40
Purchase #6	$94.45	11.719%	$105.5186	$105.52	$105.50	$105.50
Purchase #7	$173.25	12.219%	$194.4194	$194.42	$194.40	$194.40
7 purchase totals =	$864.38		$958.5787	$958.57	$958.50	$958.50