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	$241.80	13.802%	$275.1732	$275.17	$275.15	$275.20
Purchase #2	$158.25	7.786%	$170.5713	$170.57	$170.55	$170.60
Purchase #3	$190.90	10.308%	$210.578	$210.58	$210.60	$210.60
Purchase #4	$93.37	7.857%	$100.7061	$100.71	$100.70	$100.70
Purchase #5	$28.93	9.110%	$31.5655	$31.57	$31.55	$31.60
Purchase #6	$202.44	6.602%	$215.8051	$215.81	$215.80	$215.80
Purchase #7	$175.56	3.561%	$181.8117	$181.81	$181.80	$181.80
7 purchase totals =	$1,091.25		$1,186.2109	$1,186.22	$1,186.15	$1,186.30