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	$52.97	11.619%	$59.1246	$59.12	$59.10	$59.10
Purchase #2	$27.50	7.494%	$29.5609	$29.56	$29.55	$29.60
Purchase #3	$129.27	13.564%	$146.8042	$146.80	$146.80	$146.80
Purchase #4	$243.57	6.244%	$258.7785	$258.78	$258.80	$258.80
Purchase #5	$168.47	4.398%	$175.8793	$175.88	$175.90	$175.90
Purchase #6	$133.57	11.393%	$148.7876	$148.79	$148.80	$148.80
Purchase #7	$59.88	3.115%	$61.7453	$61.75	$61.75	$61.70
7 purchase totals =	$815.23		$880.6804	$880.68	$880.70	$880.70