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	$122.77	13.698%	$139.587	$139.59	$139.60	$139.60
Purchase #2	$110.54	11.766%	$123.5461	$123.55	$123.55	$123.50
Purchase #3	$219.49	10.570%	$242.6901	$242.69	$242.70	$242.70
Purchase #4	$148.65	8.554%	$161.3655	$161.37	$161.35	$161.40
Purchase #5	$84.59	7.477%	$90.9148	$90.91	$90.90	$90.90
Purchase #6	$90.95	5.774%	$96.2015	$96.20	$96.20	$96.20
Purchase #7	$188.47	5.167%	$198.2082	$198.21	$198.20	$198.20
7 purchase totals =	$965.46		$1,052.5132	$1,052.52	$1,052.50	$1,052.50