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	$85.64	5.110%	$90.0162	$90.02	$90.00	$90.00
Purchase #2	$86.41	5.110%	$90.8256	$90.83	$90.85	$90.80
Purchase #3	$126.25	9.543%	$138.298	$138.30	$138.30	$138.30
Purchase #4	$148.25	11.713%	$165.6145	$165.61	$165.60	$165.60
Purchase #5	$6.41	8.367%	$6.9463	$6.95	$6.95	$6.90
Purchase #6	$13.48	13.416%	$15.2885	$15.29	$15.30	$15.30
Purchase #7	$25.96	4.443%	$27.1134	$27.11	$27.10	$27.10
7 purchase totals =	$492.40		$534.1025	$534.11	$534.10	$534.00