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	$136.55	3.767%	$141.6938	$141.69	$141.70	$141.70
Purchase #2	$35.85	10.655%	$39.6698	$39.67	$39.65	$39.70
Purchase #3	$31.33	12.426%	$35.2231	$35.22	$35.20	$35.20
Purchase #4	$58.56	4.329%	$61.0951	$61.10	$61.10	$61.10
Purchase #5	$40.71	9.206%	$44.4578	$44.46	$44.45	$44.50
Purchase #6	$51.52	11.241%	$57.3114	$57.31	$57.30	$57.30
Purchase #7	$233.85	8.567%	$253.8839	$253.88	$253.90	$253.90
7 purchase totals =	$588.37		$633.3349	$633.33	$633.30	$633.40