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	$24.96	7.710%	$26.8844	$26.88	$26.90	$26.90
Purchase #2	$87.87	3.442%	$90.8945	$90.89	$90.90	$90.90
Purchase #3	$165.80	10.244%	$182.7846	$182.78	$182.80	$182.80
Purchase #4	$86.74	5.119%	$91.1802	$91.18	$91.20	$91.20
Purchase #5	$51.80	12.342%	$58.1932	$58.19	$58.20	$58.20
Purchase #6	$147.52	4.192%	$153.704	$153.70	$153.70	$153.70
Purchase #7	$80.36	11.575%	$89.6617	$89.66	$89.65	$89.70
7 purchase totals =	$645.05		$693.3026	$693.28	$693.35	$693.40