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	$98.73	6.662%	$105.3074	$105.31	$105.30	$105.30
Purchase #2	$161.92	5.353%	$170.5876	$170.59	$170.60	$170.60
Purchase #3	$177.55	7.162%	$190.2661	$190.27	$190.25	$190.30
Purchase #4	$218.77	10.691%	$242.1587	$242.16	$242.15	$242.20
Purchase #5	$174.90	11.712%	$195.3843	$195.38	$195.40	$195.40
Purchase #6	$86.58	4.580%	$90.5454	$90.55	$90.55	$90.50
Purchase #7	$42.43	9.376%	$46.4082	$46.41	$46.40	$46.40
7 purchase totals =	$960.88		$1,040.6577	$1,040.67	$1,040.65	$1,040.70