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	$145.32	6.671%	$155.0143	$155.01	$155.00	$155.00
Purchase #2	$141.51	5.210%	$148.8827	$148.88	$148.90	$148.90
Purchase #3	$185.93	13.125%	$210.3333	$210.33	$210.35	$210.30
Purchase #4	$59.83	10.157%	$65.9069	$65.91	$65.90	$65.90
Purchase #5	$204.61	4.337%	$213.4839	$213.48	$213.50	$213.50
Purchase #6	$83.54	9.185%	$91.2131	$91.21	$91.20	$91.20
Purchase #7	$87.78	4.196%	$91.4632	$91.46	$91.45	$91.50
7 purchase totals =	$908.52		$976.2974	$976.28	$976.30	$976.30