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	$231.63	10.308%	$255.5064	$255.51	$255.50	$255.50
Purchase #2	$27.68	5.754%	$29.2727	$29.27	$29.25	$29.30
Purchase #3	$207.77	13.356%	$235.5198	$235.52	$235.50	$235.50
Purchase #4	$130.74	6.736%	$139.5466	$139.55	$139.55	$139.50
Purchase #5	$151.49	11.222%	$168.4902	$168.49	$168.50	$168.50
Purchase #6	$82.62	4.369%	$86.2297	$86.23	$86.25	$86.20
Purchase #7	$146.56	10.504%	$161.9547	$161.95	$161.95	$162.00
7 purchase totals =	$978.49		$1,076.5201	$1,076.52	$1,076.50	$1,076.50