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	$77.62	10.284%	$85.6024	$85.60	$85.60	$85.60
Purchase #2	$28.96	6.372%	$30.8053	$30.81	$30.80	$30.80
Purchase #3	$71.25	7.427%	$76.5417	$76.54	$76.55	$76.50
Purchase #4	$87.89	12.773%	$99.1162	$99.12	$99.10	$99.10
Purchase #5	$105.83	11.321%	$117.811	$117.81	$117.80	$117.80
Purchase #6	$106.53	10.481%	$117.6954	$117.70	$117.70	$117.70
Purchase #7	$80.53	12.131%	$90.2991	$90.30	$90.30	$90.30
7 purchase totals =	$558.61		$617.8711	$617.88	$617.85	$617.80