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	$137.27	13.486%	$155.7822	$155.78	$155.80	$155.80
Purchase #2	$79.28	13.325%	$89.8441	$89.84	$89.85	$89.80
Purchase #3	$92.31	6.651%	$98.4495	$98.45	$98.45	$98.40
Purchase #4	$229.31	6.383%	$243.9469	$243.95	$243.95	$243.90
Purchase #5	$148.34	8.307%	$160.6626	$160.66	$160.65	$160.70
Purchase #6	$113.35	5.403%	$119.4743	$119.47	$119.45	$119.50
Purchase #7	$53.36	7.299%	$57.2547	$57.25	$57.25	$57.30
7 purchase totals =	$853.22		$925.4143	$925.40	$925.40	$925.40