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	$225.25	11.392%	$250.9105	$250.91	$250.90	$250.90
Purchase #2	$156.77	11.328%	$174.5289	$174.53	$174.55	$174.50
Purchase #3	$111.41	4.507%	$116.4312	$116.43	$116.45	$116.40
Purchase #4	$25.49	6.482%	$27.1423	$27.14	$27.15	$27.10
Purchase #5	$58.89	13.470%	$66.8225	$66.82	$66.80	$66.80
Purchase #6	$158.82	12.577%	$178.7948	$178.79	$178.80	$178.80
Purchase #7	$244.34	11.671%	$272.8569	$272.86	$272.85	$272.90
7 purchase totals =	$980.97		$1,087.4871	$1,087.48	$1,087.50	$1,087.40