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	$171.89	7.157%	$184.1922	$184.19	$184.20	$184.20
Purchase #2	$162.70	12.720%	$183.3954	$183.40	$183.40	$183.40
Purchase #3	$96.28	4.577%	$100.6867	$100.69	$100.70	$100.70
Purchase #4	$240.38	11.161%	$267.2088	$267.21	$267.20	$267.20
Purchase #5	$62.91	6.655%	$67.0967	$67.10	$67.10	$67.10
Purchase #6	$72.66	11.360%	$80.9142	$80.91	$80.90	$80.90
Purchase #7	$89.54	10.862%	$99.2658	$99.27	$99.25	$99.30
7 purchase totals =	$896.36		$982.7598	$982.77	$982.75	$982.80