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	$66.48	6.106%	$70.5393	$70.54	$70.55	$70.50
Purchase #2	$57.52	3.740%	$59.6712	$59.67	$59.65	$59.70
Purchase #3	$30.58	11.235%	$34.0157	$34.02	$34.00	$34.00
Purchase #4	$75.66	13.398%	$85.7969	$85.80	$85.80	$85.80
Purchase #5	$181.52	9.314%	$198.4268	$198.43	$198.45	$198.40
Purchase #6	$99.35	13.341%	$112.6043	$112.60	$112.60	$112.60
Purchase #7	$235.91	11.430%	$262.8745	$262.87	$262.85	$262.90
7 purchase totals =	$747.02		$823.9287	$823.93	$823.90	$823.90