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	$159.49	3.425%	$164.9525	$164.95	$164.95	$165.00
Purchase #2	$39.45	3.247%	$40.7309	$40.73	$40.75	$40.70
Purchase #3	$103.25	12.511%	$116.1676	$116.17	$116.15	$116.20
Purchase #4	$61.31	9.791%	$67.3129	$67.31	$67.30	$67.30
Purchase #5	$48.36	6.586%	$51.545	$51.55	$51.55	$51.50
Purchase #6	$196.68	6.322%	$209.1141	$209.11	$209.10	$209.10
Purchase #7	$247.81	9.152%	$270.4896	$270.49	$270.50	$270.50
7 purchase totals =	$856.35		$920.3126	$920.31	$920.30	$920.30