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	$71.89	10.865%	$79.7008	$79.70	$79.70	$79.70
Purchase #2	$168.93	11.442%	$188.259	$188.26	$188.25	$188.30
Purchase #3	$44.63	11.120%	$49.5929	$49.59	$49.60	$49.60
Purchase #4	$111.48	13.228%	$126.2266	$126.23	$126.25	$126.20
Purchase #5	$156.97	6.332%	$166.9093	$166.91	$166.90	$166.90
Purchase #6	$60.67	11.710%	$67.7745	$67.77	$67.75	$67.80
Purchase #7	$151.31	11.359%	$168.4973	$168.50	$168.50	$168.50
7 purchase totals =	$765.88		$846.9604	$846.96	$846.95	$847.00