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	$85.79	6.345%	$91.2334	$91.23	$91.25	$91.20
Purchase #2	$187.90	13.566%	$213.3905	$213.39	$213.40	$213.40
Purchase #3	$69.63	9.315%	$76.116	$76.12	$76.10	$76.10
Purchase #4	$93.62	10.194%	$103.1636	$103.16	$103.15	$103.20
Purchase #5	$160.37	3.755%	$166.3919	$166.39	$166.40	$166.40
Purchase #6	$150.83	4.680%	$157.8888	$157.89	$157.90	$157.90
Purchase #7	$72.29	8.696%	$78.5763	$78.58	$78.60	$78.60
7 purchase totals =	$820.43		$886.7605	$886.76	$886.80	$886.80