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	$172.60	5.622%	$182.3036	$182.30	$182.30	$182.30
Purchase #2	$222.90	10.782%	$246.9331	$246.93	$246.95	$246.90
Purchase #3	$188.79	11.668%	$210.818	$210.82	$210.80	$210.80
Purchase #4	$90.27	13.415%	$102.3797	$102.38	$102.40	$102.40
Purchase #5	$129.71	6.232%	$137.7935	$137.79	$137.80	$137.80
Purchase #6	$63.57	13.503%	$72.1539	$72.15	$72.15	$72.20
Purchase #7	$194.64	9.225%	$212.5955	$212.60	$212.60	$212.60
7 purchase totals =	$1,062.48		$1,164.9773	$1,164.97	$1,165.00	$1,165.00