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	$248.67	10.804%	$275.5363	$275.54	$275.55	$275.50
Purchase #2	$41.48	3.360%	$42.8737	$42.87	$42.85	$42.90
Purchase #3	$132.87	10.320%	$146.5822	$146.58	$146.60	$146.60
Purchase #4	$180.66	9.719%	$198.2183	$198.22	$198.20	$198.20
Purchase #5	$110.72	10.220%	$122.0356	$122.04	$122.05	$122.00
Purchase #6	$86.78	4.415%	$90.6113	$90.61	$90.60	$90.60
Purchase #7	$68.69	7.569%	$73.8891	$73.89	$73.90	$73.90
7 purchase totals =	$869.87		$949.7465	$949.75	$949.75	$949.70