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	$88.63	12.338%	$99.5652	$99.57	$99.55	$99.60
Purchase #2	$116.95	3.547%	$121.0982	$121.10	$121.10	$121.10
Purchase #3	$58.37	7.223%	$62.5861	$62.59	$62.60	$62.60
Purchase #4	$168.64	8.865%	$183.5899	$183.59	$183.60	$183.60
Purchase #5	$96.89	9.426%	$106.0229	$106.02	$106.00	$106.00
Purchase #6	$194.50	8.546%	$211.122	$211.12	$211.10	$211.10
Purchase #7	$81.91	10.572%	$90.5695	$90.57	$90.55	$90.60
7 purchase totals =	$805.89		$874.5538	$874.56	$874.50	$874.60