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	$143.46	8.113%	$155.0989	$155.10	$155.10	$155.10
Purchase #2	$240.58	13.745%	$273.6477	$273.65	$273.65	$273.60
Purchase #3	$56.77	12.558%	$63.8992	$63.90	$63.90	$63.90
Purchase #4	$134.58	4.692%	$140.8945	$140.89	$140.90	$140.90
Purchase #5	$209.54	6.187%	$222.5042	$222.50	$222.50	$222.50
Purchase #6	$110.80	10.446%	$122.3742	$122.37	$122.35	$122.40
Purchase #7	$91.61	8.323%	$99.2347	$99.23	$99.25	$99.20
7 purchase totals =	$987.34		$1,077.6534	$1,077.64	$1,077.65	$1,077.60