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	$78.74	6.546%	$83.8943	$83.89	$83.90	$83.90
Purchase #2	$100.56	10.406%	$111.0243	$111.02	$111.00	$111.00
Purchase #3	$221.40	3.140%	$228.352	$228.35	$228.35	$228.40
Purchase #4	$26.47	13.734%	$30.1054	$30.11	$30.10	$30.10
Purchase #5	$52.31	8.165%	$56.5811	$56.58	$56.60	$56.60
Purchase #6	$55.35	8.136%	$59.8533	$59.85	$59.85	$59.90
Purchase #7	$41.55	12.307%	$46.6636	$46.66	$46.65	$46.70
7 purchase totals =	$576.38		$616.4740	$616.46	$616.45	$616.60