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	$117.43	9.451%	$128.5283	$128.53	$128.55	$128.50
Purchase #2	$168.29	10.227%	$185.501	$185.50	$185.50	$185.50
Purchase #3	$73.56	11.805%	$82.2438	$82.24	$82.25	$82.20
Purchase #4	$26.78	4.390%	$27.9556	$27.96	$27.95	$28.00
Purchase #5	$162.50	12.692%	$183.1245	$183.12	$183.10	$183.10
Purchase #6	$229.63	3.472%	$237.6028	$237.60	$237.60	$237.60
Purchase #7	$66.35	6.823%	$70.8771	$70.88	$70.90	$70.90
7 purchase totals =	$844.54		$915.8331	$915.83	$915.85	$915.80