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	$116.84	6.425%	$124.347	$124.35	$124.35	$124.30
Purchase #2	$22.67	10.237%	$24.9907	$24.99	$25.00	$25.00
Purchase #3	$39.59	9.350%	$43.2917	$43.29	$43.30	$43.30
Purchase #4	$56.91	4.146%	$59.2695	$59.27	$59.25	$59.30
Purchase #5	$127.98	8.268%	$138.5614	$138.56	$138.55	$138.60
Purchase #6	$73.89	11.750%	$82.5721	$82.57	$82.55	$82.60
Purchase #7	$175.88	9.104%	$191.8921	$191.89	$191.90	$191.90
7 purchase totals =	$613.76		$664.9245	$664.92	$664.90	$665.00