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	$115.64	3.673%	$119.8875	$119.89	$119.90	$119.90
Purchase #2	$98.81	12.171%	$110.8362	$110.84	$110.85	$110.80
Purchase #3	$70.29	11.842%	$78.6137	$78.61	$78.60	$78.60
Purchase #4	$231.46	9.499%	$253.4464	$253.45	$253.45	$253.40
Purchase #5	$213.34	5.593%	$225.2721	$225.27	$225.25	$225.30
Purchase #6	$217.82	7.611%	$234.3983	$234.40	$234.40	$234.40
Purchase #7	$19.26	11.221%	$21.4212	$21.42	$21.40	$21.40
7 purchase totals =	$966.62		$1,043.8754	$1,043.88	$1,043.85	$1,043.80