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	$81.46	10.811%	$90.2666	$90.27	$90.25	$90.30
Purchase #2	$193.39	5.218%	$203.4811	$203.48	$203.50	$203.50
Purchase #3	$211.52	13.842%	$240.7986	$240.80	$240.80	$240.80
Purchase #4	$42.33	10.151%	$46.6269	$46.63	$46.65	$46.60
Purchase #5	$196.75	11.232%	$218.849	$218.85	$218.85	$218.80
Purchase #6	$71.89	10.559%	$79.4809	$79.48	$79.50	$79.50
Purchase #7	$130.54	12.343%	$146.6526	$146.65	$146.65	$146.70
7 purchase totals =	$927.88		$1,026.1557	$1,026.16	$1,026.20	$1,026.20