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	$26.59	8.111%	$28.7467	$28.75	$28.75	$28.70
Purchase #2	$121.40	8.221%	$131.3803	$131.38	$131.40	$131.40
Purchase #3	$153.50	5.833%	$162.4537	$162.45	$162.45	$162.50
Purchase #4	$77.75	9.451%	$85.0982	$85.10	$85.10	$85.10
Purchase #5	$191.61	3.799%	$198.8893	$198.89	$198.90	$198.90
Purchase #6	$91.56	10.716%	$101.3716	$101.37	$101.35	$101.40
Purchase #7	$167.88	12.845%	$189.4442	$189.44	$189.45	$189.40
7 purchase totals =	$830.29		$897.3840	$897.38	$897.40	$897.40