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	$13.32	11.262%	$14.8201	$14.82	$14.80	$14.80
Purchase #2	$222.98	12.398%	$250.6251	$250.63	$250.65	$250.60
Purchase #3	$98.90	13.103%	$111.8589	$111.86	$111.85	$111.90
Purchase #4	$160.51	7.764%	$172.972	$172.97	$172.95	$173.00
Purchase #5	$72.35	11.834%	$80.9119	$80.91	$80.90	$80.90
Purchase #6	$203.86	7.288%	$218.7173	$218.72	$218.70	$218.70
Purchase #7	$129.86	9.187%	$141.7902	$141.79	$141.80	$141.80
7 purchase totals =	$901.78		$991.6955	$991.70	$991.65	$991.70