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	$58.91	9.665%	$64.6037	$64.60	$64.60	$64.60
Purchase #2	$55.99	3.170%	$57.7649	$57.76	$57.75	$57.80
Purchase #3	$191.71	6.353%	$203.8893	$203.89	$203.90	$203.90
Purchase #4	$215.37	7.411%	$231.3311	$231.33	$231.35	$231.30
Purchase #5	$177.72	10.794%	$196.9031	$196.90	$196.90	$196.90
Purchase #6	$85.45	4.168%	$89.0116	$89.01	$89.00	$89.00
Purchase #7	$29.76	4.744%	$31.1718	$31.17	$31.15	$31.20
7 purchase totals =	$814.91		$874.6755	$874.66	$874.65	$874.70