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	$76.58	7.870%	$82.6068	$82.61	$82.60	$82.60
Purchase #2	$71.75	13.230%	$81.2425	$81.24	$81.25	$81.20
Purchase #3	$76.81	4.107%	$79.9646	$79.96	$79.95	$80.00
Purchase #4	$149.96	10.162%	$165.1989	$165.20	$165.20	$165.20
Purchase #5	$230.83	4.299%	$240.7534	$240.75	$240.75	$240.80
Purchase #6	$99.53	4.730%	$104.2378	$104.24	$104.25	$104.20
Purchase #7	$237.54	7.738%	$255.9208	$255.92	$255.90	$255.90
7 purchase totals =	$943.00		$1,009.9248	$1,009.92	$1,009.90	$1,009.90