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	$81.56	6.472%	$86.8386	$86.84	$86.85	$86.80
Purchase #2	$113.79	5.721%	$120.2999	$120.30	$120.30	$120.30
Purchase #3	$152.56	12.705%	$171.9427	$171.94	$171.95	$171.90
Purchase #4	$101.52	10.411%	$112.0892	$112.09	$112.10	$112.10
Purchase #5	$91.84	9.821%	$100.8596	$100.86	$100.85	$100.90
Purchase #6	$144.53	7.515%	$155.3914	$155.39	$155.40	$155.40
Purchase #7	$89.30	4.318%	$93.156	$93.16	$93.15	$93.20
7 purchase totals =	$775.10		$840.5774	$840.58	$840.60	$840.60