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	$232.70	3.862%	$241.6869	$241.69	$241.70	$241.70
Purchase #2	$183.84	9.819%	$201.8912	$201.89	$201.90	$201.90
Purchase #3	$119.55	3.349%	$123.5537	$123.55	$123.55	$123.60
Purchase #4	$152.44	3.852%	$158.312	$158.31	$158.30	$158.30
Purchase #5	$37.99	12.671%	$42.8037	$42.80	$42.80	$42.80
Purchase #6	$77.40	3.389%	$80.0231	$80.02	$80.00	$80.00
Purchase #7	$72.26	8.754%	$78.5856	$78.59	$78.60	$78.60
7 purchase totals =	$876.18		$926.8562	$926.85	$926.85	$926.90