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	$116.28	11.846%	$130.0545	$130.05	$130.05	$130.10
Purchase #2	$105.86	3.549%	$109.617	$109.62	$109.60	$109.60
Purchase #3	$101.44	3.511%	$105.0016	$105.00	$105.00	$105.00
Purchase #4	$56.36	5.234%	$59.3099	$59.31	$59.30	$59.30
Purchase #5	$80.47	11.766%	$89.9381	$89.94	$89.95	$89.90
Purchase #6	$52.39	13.154%	$59.2814	$59.28	$59.30	$59.30
Purchase #7	$56.56	13.106%	$63.9728	$63.97	$63.95	$64.00
7 purchase totals =	$569.36		$617.1753	$617.17	$617.15	$617.20