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	$10.90	7.424%	$11.7092	$11.71	$11.70	$11.70
Purchase #2	$93.94	11.794%	$105.0193	$105.02	$105.00	$105.00
Purchase #3	$77.33	7.164%	$82.8699	$82.87	$82.85	$82.90
Purchase #4	$141.39	9.176%	$154.3639	$154.36	$154.35	$154.40
Purchase #5	$246.39	4.126%	$256.5561	$256.56	$256.55	$256.60
Purchase #6	$146.33	3.207%	$151.0228	$151.02	$151.00	$151.00
Purchase #7	$52.28	6.794%	$55.8319	$55.83	$55.85	$55.80
7 purchase totals =	$768.56		$817.3731	$817.37	$817.30	$817.40