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	$101.71	3.828%	$105.6035	$105.60	$105.60	$105.60
Purchase #2	$238.47	8.252%	$258.1485	$258.15	$258.15	$258.10
Purchase #3	$222.85	12.790%	$251.3525	$251.35	$251.35	$251.40
Purchase #4	$55.57	12.240%	$62.3718	$62.37	$62.35	$62.40
Purchase #5	$35.85	12.302%	$40.2603	$40.26	$40.25	$40.30
Purchase #6	$238.46	13.276%	$270.1179	$270.12	$270.10	$270.10
Purchase #7	$151.97	10.731%	$168.2779	$168.28	$168.30	$168.30
7 purchase totals =	$1,044.88		$1,156.1324	$1,156.13	$1,156.10	$1,156.20