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	$83.35	9.553%	$91.3124	$91.31	$91.30	$91.30
Purchase #2	$127.51	9.223%	$139.2702	$139.27	$139.25	$139.30
Purchase #3	$41.42	13.345%	$46.9475	$46.95	$46.95	$46.90
Purchase #4	$195.86	10.153%	$215.7457	$215.75	$215.75	$215.70
Purchase #5	$208.69	12.590%	$234.9641	$234.96	$234.95	$235.00
Purchase #6	$35.85	12.803%	$40.4399	$40.44	$40.45	$40.40
Purchase #7	$105.85	9.218%	$115.6073	$115.61	$115.60	$115.60
7 purchase totals =	$798.53		$884.2871	$884.29	$884.25	$884.20