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	$126.69	10.359%	$139.8138	$139.81	$139.80	$139.80
Purchase #2	$184.78	13.606%	$209.9212	$209.92	$209.90	$209.90
Purchase #3	$135.62	7.609%	$145.9393	$145.94	$145.95	$145.90
Purchase #4	$69.92	3.158%	$72.1281	$72.13	$72.15	$72.10
Purchase #5	$81.39	12.206%	$91.3245	$91.32	$91.30	$91.30
Purchase #6	$162.58	11.472%	$181.2312	$181.23	$181.25	$181.20
Purchase #7	$90.90	11.248%	$101.1244	$101.12	$101.10	$101.10
7 purchase totals =	$851.88		$941.4825	$941.47	$941.45	$941.30