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	$165.83	9.443%	$181.4893	$181.49	$181.50	$181.50
Purchase #2	$231.37	3.507%	$239.4841	$239.48	$239.50	$239.50
Purchase #3	$106.54	10.221%	$117.4295	$117.43	$117.45	$117.40
Purchase #4	$170.41	7.139%	$182.5756	$182.58	$182.60	$182.60
Purchase #5	$238.31	10.477%	$263.2777	$263.28	$263.30	$263.30
Purchase #6	$16.69	11.285%	$18.5735	$18.57	$18.55	$18.60
Purchase #7	$175.31	4.320%	$182.8834	$182.88	$182.90	$182.90
7 purchase totals =	$1,104.46		$1,185.7131	$1,185.71	$1,185.80	$1,185.80