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	$87.59	3.804%	$90.9219	$90.92	$90.90	$90.90
Purchase #2	$177.73	4.269%	$185.3173	$185.32	$185.30	$185.30
Purchase #3	$183.29	4.837%	$192.1557	$192.16	$192.15	$192.20
Purchase #4	$79.57	13.300%	$90.1528	$90.15	$90.15	$90.20
Purchase #5	$107.95	4.502%	$112.8099	$112.81	$112.80	$112.80
Purchase #6	$172.82	5.796%	$182.8366	$182.84	$182.85	$182.80
Purchase #7	$193.29	5.388%	$203.7045	$203.70	$203.70	$203.70
7 purchase totals =	$1,002.24		$1,057.8987	$1,057.90	$1,057.85	$1,057.90