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	$150.40	6.480%	$160.1459	$160.15	$160.15	$160.10
Purchase #2	$239.47	6.789%	$255.7276	$255.73	$255.75	$255.70
Purchase #3	$200.79	8.522%	$217.9013	$217.90	$217.90	$217.90
Purchase #4	$211.80	5.222%	$222.8602	$222.86	$222.85	$222.90
Purchase #5	$37.79	6.656%	$40.3053	$40.31	$40.30	$40.30
Purchase #6	$221.97	12.606%	$249.9515	$249.95	$249.95	$250.00
Purchase #7	$88.27	9.437%	$96.6	$96.60	$96.60	$96.60
7 purchase totals =	$1,150.49		$1,243.4918	$1,243.50	$1,243.50	$1,243.50