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	$84.42	7.252%	$90.5421	$90.54	$90.55	$90.50
Purchase #2	$117.90	11.781%	$131.7898	$131.79	$131.80	$131.80
Purchase #3	$127.94	12.341%	$143.7291	$143.73	$143.75	$143.70
Purchase #4	$141.92	8.170%	$153.5149	$153.51	$153.50	$153.50
Purchase #5	$37.29	13.175%	$42.203	$42.20	$42.20	$42.20
Purchase #6	$112.62	4.693%	$117.9053	$117.91	$117.90	$117.90
Purchase #7	$89.87	12.824%	$101.3949	$101.39	$101.40	$101.40
7 purchase totals =	$711.96		$781.0791	$781.07	$781.10	$781.00