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	$17.84	4.863%	$18.7076	$18.71	$18.70	$18.70
Purchase #2	$131.45	6.139%	$139.5197	$139.52	$139.50	$139.50
Purchase #3	$149.55	5.662%	$158.0175	$158.02	$158.00	$158.00
Purchase #4	$109.31	12.319%	$122.7759	$122.78	$122.80	$122.80
Purchase #5	$46.30	11.127%	$51.4518	$51.45	$51.45	$51.50
Purchase #6	$6.73	12.545%	$7.5743	$7.57	$7.55	$7.60
Purchase #7	$68.86	10.614%	$76.1688	$76.17	$76.15	$76.20
7 purchase totals =	$530.04		$574.2156	$574.22	$574.15	$574.30