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	$80.35	10.568%	$88.8414	$88.84	$88.85	$88.80
Purchase #2	$104.40	5.126%	$109.7515	$109.75	$109.75	$109.80
Purchase #3	$78.40	4.232%	$81.7179	$81.72	$81.70	$81.70
Purchase #4	$63.45	5.862%	$67.1694	$67.17	$67.15	$67.20
Purchase #5	$144.71	4.173%	$150.7487	$150.75	$150.75	$150.70
Purchase #6	$55.77	12.426%	$62.7	$62.70	$62.70	$62.70
Purchase #7	$216.83	4.811%	$227.2617	$227.26	$227.25	$227.30
7 purchase totals =	$743.91		$788.1906	$788.19	$788.15	$788.20