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	$173.45	8.630%	$188.4187	$188.42	$188.40	$188.40
Purchase #2	$189.78	8.566%	$206.0366	$206.04	$206.05	$206.00
Purchase #3	$161.90	3.724%	$167.9292	$167.93	$167.95	$167.90
Purchase #4	$173.56	12.702%	$195.6056	$195.61	$195.60	$195.60
Purchase #5	$73.73	5.676%	$77.9149	$77.91	$77.90	$77.90
Purchase #6	$40.40	4.633%	$42.2717	$42.27	$42.25	$42.30
Purchase #7	$88.64	12.372%	$99.6065	$99.61	$99.60	$99.60
7 purchase totals =	$901.46		$977.7832	$977.79	$977.75	$977.70