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	$36.67	7.553%	$39.4397	$39.44	$39.45	$39.40
Purchase #2	$150.27	13.337%	$170.3115	$170.31	$170.30	$170.30
Purchase #3	$26.54	11.865%	$29.689	$29.69	$29.70	$29.70
Purchase #4	$69.88	6.279%	$74.2678	$74.27	$74.25	$74.30
Purchase #5	$14.44	4.127%	$15.0359	$15.04	$15.05	$15.00
Purchase #6	$82.92	7.484%	$89.1257	$89.13	$89.15	$89.10
Purchase #7	$53.38	11.229%	$59.374	$59.37	$59.35	$59.40
7 purchase totals =	$434.10		$477.2436	$477.25	$477.25	$477.20