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	$198.48	9.107%	$216.5556	$216.56	$216.55	$216.60
Purchase #2	$109.62	13.476%	$124.3924	$124.39	$124.40	$124.40
Purchase #3	$87.86	5.518%	$92.7081	$92.71	$92.70	$92.70
Purchase #4	$17.62	5.526%	$18.5937	$18.59	$18.60	$18.60
Purchase #5	$250.81	4.872%	$263.0295	$263.03	$263.05	$263.00
Purchase #6	$111.54	7.328%	$119.7137	$119.71	$119.70	$119.70
Purchase #7	$73.57	6.447%	$78.3131	$78.31	$78.30	$78.30
7 purchase totals =	$849.50		$913.3061	$913.30	$913.30	$913.30