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	$37.77	13.761%	$42.9675	$42.97	$42.95	$43.00
Purchase #2	$66.58	12.494%	$74.8985	$74.90	$74.90	$74.90
Purchase #3	$64.36	7.745%	$69.3447	$69.34	$69.35	$69.30
Purchase #4	$226.41	5.466%	$238.7856	$238.79	$238.80	$238.80
Purchase #5	$240.96	6.205%	$255.9116	$255.91	$255.90	$255.90
Purchase #6	$250.43	5.763%	$264.8623	$264.86	$264.85	$264.90
Purchase #7	$183.81	13.772%	$209.1243	$209.12	$209.10	$209.10
7 purchase totals =	$1,070.32		$1,155.8945	$1,155.89	$1,155.85	$1,155.90