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	$34.33	11.191%	$38.1719	$38.17	$38.15	$38.20
Purchase #2	$103.98	9.339%	$113.6907	$113.69	$113.70	$113.70
Purchase #3	$188.73	11.239%	$209.9414	$209.94	$209.95	$209.90
Purchase #4	$200.60	7.455%	$215.5547	$215.55	$215.55	$215.60
Purchase #5	$179.39	13.194%	$203.0587	$203.06	$203.05	$203.10
Purchase #6	$149.49	12.729%	$168.5186	$168.52	$168.50	$168.50
Purchase #7	$173.90	9.780%	$190.9074	$190.91	$190.90	$190.90
7 purchase totals =	$1,030.42		$1,139.8434	$1,139.84	$1,139.80	$1,139.90