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	$83.39	6.664%	$88.9471	$88.95	$88.95	$88.90
Purchase #2	$43.40	13.517%	$49.2664	$49.27	$49.25	$49.30
Purchase #3	$138.89	6.801%	$148.3359	$148.34	$148.35	$148.30
Purchase #4	$117.69	5.303%	$123.9311	$123.93	$123.95	$123.90
Purchase #5	$198.49	5.722%	$209.8476	$209.85	$209.85	$209.80
Purchase #6	$115.55	12.855%	$130.404	$130.40	$130.40	$130.40
Purchase #7	$195.90	11.492%	$218.4128	$218.41	$218.40	$218.40
7 purchase totals =	$893.31		$969.1449	$969.15	$969.15	$969.00