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	$195.69	11.484%	$218.163	$218.16	$218.15	$218.20
Purchase #2	$116.68	11.539%	$130.1437	$130.14	$130.15	$130.10
Purchase #3	$120.33	13.260%	$136.2858	$136.29	$136.30	$136.30
Purchase #4	$205.67	6.136%	$218.2899	$218.29	$218.30	$218.30
Purchase #5	$71.46	8.458%	$77.5041	$77.50	$77.50	$77.50
Purchase #6	$38.95	10.209%	$42.9264	$42.93	$42.95	$42.90
Purchase #7	$12.81	5.745%	$13.5459	$13.55	$13.55	$13.50
7 purchase totals =	$761.59		$836.8588	$836.86	$836.90	$836.80