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	$166.34	6.425%	$177.0273	$177.03	$177.05	$177.00
Purchase #2	$229.80	3.795%	$238.5209	$238.52	$238.50	$238.50
Purchase #3	$99.68	8.511%	$108.1638	$108.16	$108.15	$108.20
Purchase #4	$33.69	11.768%	$37.6546	$37.65	$37.65	$37.70
Purchase #5	$203.33	11.658%	$227.0342	$227.03	$227.05	$227.00
Purchase #6	$97.63	13.773%	$111.0766	$111.08	$111.10	$111.10
Purchase #7	$119.66	9.795%	$131.3807	$131.38	$131.40	$131.40
7 purchase totals =	$950.13		$1,030.8581	$1,030.85	$1,030.90	$1,030.90