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	$239.76	12.833%	$270.5284	$270.53	$270.55	$270.50
Purchase #2	$24.34	3.708%	$25.2425	$25.24	$25.25	$25.20
Purchase #3	$38.46	6.237%	$40.8588	$40.86	$40.85	$40.90
Purchase #4	$241.87	9.325%	$264.4244	$264.42	$264.40	$264.40
Purchase #5	$131.65	11.165%	$146.3487	$146.35	$146.35	$146.30
Purchase #6	$92.42	7.743%	$99.5761	$99.58	$99.60	$99.60
Purchase #7	$59.31	11.419%	$66.0826	$66.08	$66.10	$66.10
7 purchase totals =	$827.81		$913.0615	$913.06	$913.10	$913.00