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	$81.79	9.111%	$89.2419	$89.24	$89.25	$89.20
Purchase #2	$118.42	4.414%	$123.6471	$123.65	$123.65	$123.60
Purchase #3	$69.80	10.461%	$77.1018	$77.10	$77.10	$77.10
Purchase #4	$85.89	6.597%	$91.5562	$91.56	$91.55	$91.60
Purchase #5	$172.91	6.141%	$183.5284	$183.53	$183.55	$183.50
Purchase #6	$139.93	10.422%	$154.5135	$154.51	$154.50	$154.50
Purchase #7	$79.32	9.656%	$86.9791	$86.98	$87.00	$87.00
7 purchase totals =	$748.06		$806.5680	$806.57	$806.60	$806.50