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	$230.85	8.234%	$249.8582	$249.86	$249.85	$249.90
Purchase #2	$210.49	4.375%	$219.6989	$219.70	$219.70	$219.70
Purchase #3	$158.44	6.126%	$168.146	$168.15	$168.15	$168.10
Purchase #4	$6.46	5.730%	$6.8302	$6.83	$6.85	$6.80
Purchase #5	$151.42	4.393%	$158.0719	$158.07	$158.05	$158.10
Purchase #6	$94.40	6.419%	$100.4595	$100.46	$100.45	$100.50
Purchase #7	$66.59	10.284%	$73.4381	$73.44	$73.45	$73.40
7 purchase totals =	$918.65		$976.5028	$976.51	$976.50	$976.50