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	$172.49	7.760%	$185.8752	$185.88	$185.90	$185.90
Purchase #2	$231.85	11.813%	$259.2384	$259.24	$259.25	$259.20
Purchase #3	$109.39	9.361%	$119.63	$119.63	$119.65	$119.60
Purchase #4	$62.43	6.269%	$66.3437	$66.34	$66.35	$66.30
Purchase #5	$146.60	6.625%	$156.3123	$156.31	$156.30	$156.30
Purchase #6	$82.79	9.792%	$90.8968	$90.90	$90.90	$90.90
Purchase #7	$19.99	12.847%	$22.5581	$22.56	$22.55	$22.60
7 purchase totals =	$825.54		$900.8545	$900.86	$900.90	$900.80