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	$242.90	12.390%	$272.9953	$273.00	$273.00	$273.00
Purchase #2	$178.38	9.554%	$195.4224	$195.42	$195.40	$195.40
Purchase #3	$189.44	3.625%	$196.3072	$196.31	$196.30	$196.30
Purchase #4	$57.37	5.787%	$60.69	$60.69	$60.70	$60.70
Purchase #5	$132.86	6.429%	$141.4016	$141.40	$141.40	$141.40
Purchase #6	$114.56	7.288%	$122.9091	$122.91	$122.90	$122.90
Purchase #7	$26.47	4.241%	$27.5926	$27.59	$27.60	$27.60
7 purchase totals =	$941.98		$1,017.3182	$1,017.32	$1,017.30	$1,017.30