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	$38.25	11.103%	$42.4969	$42.50	$42.50	$42.50
Purchase #2	$77.28	13.814%	$87.9555	$87.96	$87.95	$88.00
Purchase #3	$139.54	7.788%	$150.4074	$150.41	$150.40	$150.40
Purchase #4	$40.66	5.433%	$42.8691	$42.87	$42.85	$42.90
Purchase #5	$76.98	4.508%	$80.4503	$80.45	$80.45	$80.50
Purchase #6	$172.99	5.623%	$182.7172	$182.72	$182.70	$182.70
Purchase #7	$57.61	10.864%	$63.8688	$63.87	$63.85	$63.90
7 purchase totals =	$603.31		$650.7652	$650.78	$650.70	$650.90