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	$210.96	9.273%	$230.5223	$230.52	$230.50	$230.50
Purchase #2	$91.32	10.445%	$100.8584	$100.86	$100.85	$100.90
Purchase #3	$108.65	10.593%	$120.1593	$120.16	$120.15	$120.20
Purchase #4	$235.55	6.774%	$251.5062	$251.51	$251.50	$251.50
Purchase #5	$196.98	7.185%	$211.133	$211.13	$211.15	$211.10
Purchase #6	$169.49	8.515%	$183.9221	$183.92	$183.90	$183.90
Purchase #7	$131.94	3.713%	$136.8389	$136.84	$136.85	$136.80
7 purchase totals =	$1,144.89		$1,234.9402	$1,234.94	$1,234.90	$1,234.90