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	$59.41	13.851%	$67.6389	$67.64	$67.65	$67.60
Purchase #2	$241.75	9.499%	$264.7138	$264.71	$264.70	$264.70
Purchase #3	$141.57	11.726%	$158.1705	$158.17	$158.15	$158.20
Purchase #4	$240.49	12.373%	$270.2458	$270.25	$270.25	$270.20
Purchase #5	$41.81	3.153%	$43.1283	$43.13	$43.15	$43.10
Purchase #6	$50.37	4.730%	$52.7525	$52.75	$52.75	$52.80
Purchase #7	$104.74	4.838%	$109.8073	$109.81	$109.80	$109.80
7 purchase totals =	$880.14		$966.4571	$966.46	$966.45	$966.40