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	$143.91	7.580%	$154.8184	$154.82	$154.80	$154.80
Purchase #2	$133.79	10.269%	$147.5289	$147.53	$147.55	$147.50
Purchase #3	$46.50	9.530%	$50.9315	$50.93	$50.95	$50.90
Purchase #4	$221.31	11.813%	$247.4534	$247.45	$247.45	$247.50
Purchase #5	$56.39	6.155%	$59.8608	$59.86	$59.85	$59.90
Purchase #6	$247.55	11.665%	$276.4267	$276.43	$276.45	$276.40
Purchase #7	$240.89	6.182%	$255.7818	$255.78	$255.80	$255.80
7 purchase totals =	$1,090.34		$1,192.8015	$1,192.80	$1,192.85	$1,192.80