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	$87.67	3.651%	$90.8708	$90.87	$90.85	$90.90
Purchase #2	$60.46	8.706%	$65.7236	$65.72	$65.70	$65.70
Purchase #3	$151.95	10.471%	$167.8607	$167.86	$167.85	$167.90
Purchase #4	$52.30	8.147%	$56.5609	$56.56	$56.55	$56.60
Purchase #5	$73.75	7.519%	$79.2953	$79.30	$79.30	$79.30
Purchase #6	$98.82	12.179%	$110.8553	$110.86	$110.85	$110.90
Purchase #7	$135.95	7.109%	$145.6147	$145.61	$145.60	$145.60
7 purchase totals =	$660.90		$716.7813	$716.78	$716.70	$716.90