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	$105.94	9.625%	$116.1367	$116.14	$116.15	$116.10
Purchase #2	$42.51	8.803%	$46.2522	$46.25	$46.25	$46.30
Purchase #3	$113.76	6.230%	$120.8472	$120.85	$120.85	$120.80
Purchase #4	$216.94	5.300%	$228.4378	$228.44	$228.45	$228.40
Purchase #5	$139.32	8.241%	$150.8014	$150.80	$150.80	$150.80
Purchase #6	$70.56	10.735%	$78.1346	$78.13	$78.15	$78.10
Purchase #7	$85.73	4.181%	$89.3144	$89.31	$89.30	$89.30
7 purchase totals =	$774.76		$829.9243	$829.92	$829.95	$829.80