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	$239.87	13.260%	$271.6768	$271.68	$271.70	$271.70
Purchase #2	$153.78	8.138%	$166.2946	$166.29	$166.30	$166.30
Purchase #3	$24.36	10.734%	$26.9748	$26.97	$26.95	$27.00
Purchase #4	$61.33	8.238%	$66.3824	$66.38	$66.40	$66.40
Purchase #5	$159.55	5.854%	$168.8901	$168.89	$168.90	$168.90
Purchase #6	$182.98	7.296%	$196.3302	$196.33	$196.35	$196.30
Purchase #7	$54.45	12.312%	$61.1539	$61.15	$61.15	$61.20
7 purchase totals =	$876.32		$957.7028	$957.69	$957.75	$957.80