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	$133.91	10.649%	$148.1701	$148.17	$148.15	$148.20
Purchase #2	$236.71	5.225%	$249.0781	$249.08	$249.10	$249.10
Purchase #3	$145.35	9.275%	$158.8312	$158.83	$158.85	$158.80
Purchase #4	$145.47	7.865%	$156.9112	$156.91	$156.90	$156.90
Purchase #5	$139.34	10.873%	$154.4904	$154.49	$154.50	$154.50
Purchase #6	$92.88	7.217%	$99.5831	$99.58	$99.60	$99.60
Purchase #7	$34.69	5.484%	$36.5924	$36.59	$36.60	$36.60
7 purchase totals =	$928.35		$1,003.6565	$1,003.65	$1,003.70	$1,003.70