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	$140.66	6.545%	$149.8662	$149.87	$149.85	$149.90
Purchase #2	$173.48	6.227%	$184.2826	$184.28	$184.30	$184.30
Purchase #3	$183.82	4.225%	$191.5864	$191.59	$191.60	$191.60
Purchase #4	$202.59	6.280%	$215.3127	$215.31	$215.30	$215.30
Purchase #5	$78.32	5.481%	$82.6127	$82.61	$82.60	$82.60
Purchase #6	$86.50	4.256%	$90.1814	$90.18	$90.20	$90.20
Purchase #7	$75.54	3.816%	$78.4226	$78.42	$78.40	$78.40
7 purchase totals =	$940.91		$992.2646	$992.26	$992.25	$992.30