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	$234.81	12.256%	$263.5883	$263.59	$263.60	$263.60
Purchase #2	$169.38	11.264%	$188.459	$188.46	$188.45	$188.50
Purchase #3	$91.37	8.865%	$99.47	$99.47	$99.45	$99.50
Purchase #4	$160.34	8.228%	$173.5328	$173.53	$173.55	$173.50
Purchase #5	$37.61	9.315%	$41.1134	$41.11	$41.10	$41.10
Purchase #6	$150.56	8.485%	$163.335	$163.34	$163.35	$163.30
Purchase #7	$198.69	9.806%	$218.1735	$218.17	$218.15	$218.20
7 purchase totals =	$1,042.76		$1,147.6720	$1,147.67	$1,147.65	$1,147.70