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	$13.43	12.296%	$15.0814	$15.08	$15.10	$15.10
Purchase #2	$73.60	11.165%	$81.8174	$81.82	$81.80	$81.80
Purchase #3	$47.64	5.651%	$50.3321	$50.33	$50.35	$50.30
Purchase #4	$56.50	5.325%	$59.5086	$59.51	$59.50	$59.50
Purchase #5	$207.59	7.387%	$222.9247	$222.92	$222.90	$222.90
Purchase #6	$90.90	3.616%	$94.1869	$94.19	$94.20	$94.20
Purchase #7	$58.31	13.618%	$66.2507	$66.25	$66.25	$66.30
7 purchase totals =	$547.97		$590.1018	$590.10	$590.10	$590.10