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	$113.82	12.769%	$128.3537	$128.35	$128.35	$128.40
Purchase #2	$52.74	8.867%	$57.4165	$57.42	$57.40	$57.40
Purchase #3	$98.48	6.107%	$104.4942	$104.49	$104.50	$104.50
Purchase #4	$163.47	4.871%	$171.4326	$171.43	$171.45	$171.40
Purchase #5	$249.71	6.357%	$265.5841	$265.58	$265.60	$265.60
Purchase #6	$220.74	9.311%	$241.2931	$241.29	$241.30	$241.30
Purchase #7	$145.25	4.580%	$151.9025	$151.90	$151.90	$151.90
7 purchase totals =	$1,044.21		$1,120.4767	$1,120.46	$1,120.50	$1,120.50