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	$33.56	9.792%	$36.8462	$36.85	$36.85	$36.80
Purchase #2	$136.59	12.276%	$153.3578	$153.36	$153.35	$153.40
Purchase #3	$36.26	11.261%	$40.3432	$40.34	$40.35	$40.30
Purchase #4	$188.62	9.852%	$207.2028	$207.20	$207.20	$207.20
Purchase #5	$187.56	13.298%	$212.5017	$212.50	$212.50	$212.50
Purchase #6	$107.89	4.231%	$112.4548	$112.45	$112.45	$112.50
Purchase #7	$228.80	5.145%	$240.5718	$240.57	$240.55	$240.60
7 purchase totals =	$919.28		$1,003.2783	$1,003.27	$1,003.25	$1,003.30