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	$93.33	6.636%	$99.5234	$99.52	$99.50	$99.50
Purchase #2	$108.84	8.141%	$117.7007	$117.70	$117.70	$117.70
Purchase #3	$249.53	3.500%	$258.2636	$258.26	$258.25	$258.30
Purchase #4	$167.51	4.261%	$174.6476	$174.65	$174.65	$174.60
Purchase #5	$82.42	9.243%	$90.0381	$90.04	$90.05	$90.00
Purchase #6	$156.70	4.221%	$163.3143	$163.31	$163.30	$163.30
Purchase #7	$93.50	7.840%	$100.8304	$100.83	$100.85	$100.80
7 purchase totals =	$951.83		$1,004.3181	$1,004.31	$1,004.30	$1,004.20