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	$36.60	7.411%	$39.3124	$39.31	$39.30	$39.30
Purchase #2	$161.65	6.314%	$171.8566	$171.86	$171.85	$171.90
Purchase #3	$172.55	5.138%	$181.4156	$181.42	$181.40	$181.40
Purchase #4	$41.71	8.460%	$45.2387	$45.24	$45.25	$45.20
Purchase #5	$209.87	9.720%	$230.2694	$230.27	$230.25	$230.30
Purchase #6	$243.46	13.549%	$276.4464	$276.45	$276.45	$276.40
Purchase #7	$89.41	7.630%	$96.232	$96.23	$96.25	$96.20
7 purchase totals =	$955.25		$1,040.7711	$1,040.78	$1,040.75	$1,040.70