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	$25.51	9.768%	$28.0018	$28.00	$28.00	$28.00
Purchase #2	$148.89	12.346%	$167.272	$167.27	$167.25	$167.30
Purchase #3	$84.74	5.250%	$89.1889	$89.19	$89.20	$89.20
Purchase #4	$62.97	6.868%	$67.2948	$67.29	$67.30	$67.30
Purchase #5	$168.53	11.151%	$187.3228	$187.32	$187.30	$187.30
Purchase #6	$184.54	4.141%	$192.1818	$192.18	$192.20	$192.20
Purchase #7	$121.76	5.611%	$128.592	$128.59	$128.60	$128.60
7 purchase totals =	$796.94		$859.8541	$859.84	$859.85	$859.90