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	$27.53	3.119%	$28.3887	$28.39	$28.40	$28.40
Purchase #2	$40.80	6.792%	$43.5711	$43.57	$43.55	$43.60
Purchase #3	$158.64	7.819%	$171.0441	$171.04	$171.05	$171.00
Purchase #4	$98.28	5.721%	$103.9026	$103.90	$103.90	$103.90
Purchase #5	$38.28	7.658%	$41.2115	$41.21	$41.20	$41.20
Purchase #6	$105.50	10.637%	$116.722	$116.72	$116.70	$116.70
Purchase #7	$32.25	8.790%	$35.0848	$35.08	$35.10	$35.10
7 purchase totals =	$501.28		$539.9248	$539.91	$539.90	$539.90