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	$102.96	9.637%	$112.8823	$112.88	$112.90	$112.90
Purchase #2	$96.63	5.170%	$101.6258	$101.63	$101.65	$101.60
Purchase #3	$246.35	13.104%	$278.6317	$278.63	$278.65	$278.60
Purchase #4	$152.97	3.354%	$158.1006	$158.10	$158.10	$158.10
Purchase #5	$37.74	12.604%	$42.4967	$42.50	$42.50	$42.50
Purchase #6	$205.51	6.557%	$218.9853	$218.99	$219.00	$219.00
Purchase #7	$94.51	11.709%	$105.5762	$105.58	$105.60	$105.60
7 purchase totals =	$936.67		$1,018.2986	$1,018.31	$1,018.40	$1,018.30