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	$71.63	9.169%	$78.1978	$78.20	$78.20	$78.20
Purchase #2	$40.82	5.126%	$42.9124	$42.91	$42.90	$42.90
Purchase #3	$190.46	9.681%	$208.8984	$208.90	$208.90	$208.90
Purchase #4	$152.38	5.558%	$160.8493	$160.85	$160.85	$160.80
Purchase #5	$48.39	5.561%	$51.081	$51.08	$51.10	$51.10
Purchase #6	$151.81	12.576%	$170.9016	$170.90	$170.90	$170.90
Purchase #7	$96.47	12.367%	$108.4004	$108.40	$108.40	$108.40
7 purchase totals =	$751.96		$821.2409	$821.24	$821.25	$821.20