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	$173.36	7.647%	$186.6168	$186.62	$186.60	$186.60
Purchase #2	$90.62	6.139%	$96.1832	$96.18	$96.20	$96.20
Purchase #3	$117.58	9.391%	$128.6219	$128.62	$128.60	$128.60
Purchase #4	$53.66	10.295%	$59.1843	$59.18	$59.20	$59.20
Purchase #5	$75.62	12.647%	$85.1837	$85.18	$85.20	$85.20
Purchase #6	$148.41	6.529%	$158.0997	$158.10	$158.10	$158.10
Purchase #7	$80.25	8.277%	$86.8923	$86.89	$86.90	$86.90
7 purchase totals =	$739.50		$800.7819	$800.77	$800.80	$800.80