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	$90.69	3.339%	$93.7181	$93.72	$93.70	$93.70
Purchase #2	$179.34	10.168%	$197.5753	$197.58	$197.60	$197.60
Purchase #3	$167.34	11.675%	$186.8769	$186.88	$186.90	$186.90
Purchase #4	$245.79	10.606%	$271.8585	$271.86	$271.85	$271.90
Purchase #5	$146.31	10.466%	$161.6228	$161.62	$161.60	$161.60
Purchase #6	$77.99	11.440%	$86.9121	$86.91	$86.90	$86.90
Purchase #7	$74.45	10.337%	$82.1459	$82.15	$82.15	$82.10
7 purchase totals =	$981.91		$1,080.7096	$1,080.72	$1,080.70	$1,080.70