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	$93.93	6.711%	$100.2336	$100.23	$100.25	$100.20
Purchase #2	$140.57	12.664%	$158.3718	$158.37	$158.35	$158.40
Purchase #3	$7.27	6.324%	$7.7298	$7.73	$7.75	$7.70
Purchase #4	$78.85	9.366%	$86.2351	$86.24	$86.25	$86.20
Purchase #5	$62.29	6.301%	$66.2149	$66.21	$66.20	$66.20
Purchase #6	$88.89	8.799%	$96.7114	$96.71	$96.70	$96.70
Purchase #7	$65.46	12.265%	$73.4887	$73.49	$73.50	$73.50
7 purchase totals =	$537.26		$588.9853	$588.98	$589.00	$588.90