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	$37.82	13.366%	$42.875	$42.88	$42.90	$42.90
Purchase #2	$218.69	7.281%	$234.6128	$234.61	$234.60	$234.60
Purchase #3	$90.45	10.335%	$99.798	$99.80	$99.80	$99.80
Purchase #4	$210.32	5.772%	$222.4597	$222.46	$222.45	$222.50
Purchase #5	$220.60	5.704%	$233.183	$233.18	$233.20	$233.20
Purchase #6	$6.69	9.592%	$7.3317	$7.33	$7.35	$7.30
Purchase #7	$222.29	3.273%	$229.5656	$229.57	$229.55	$229.60
7 purchase totals =	$1,006.86		$1,069.8258	$1,069.83	$1,069.85	$1,069.90