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	$150.63	13.528%	$171.0072	$171.01	$171.00	$171.00
Purchase #2	$19.79	12.786%	$22.3203	$22.32	$22.30	$22.30
Purchase #3	$136.46	10.765%	$151.1499	$151.15	$151.15	$151.10
Purchase #4	$205.38	9.234%	$224.3448	$224.34	$224.35	$224.30
Purchase #5	$181.73	8.229%	$196.6846	$196.68	$196.70	$196.70
Purchase #6	$120.50	9.138%	$131.5113	$131.51	$131.50	$131.50
Purchase #7	$128.82	3.874%	$133.8105	$133.81	$133.80	$133.80
7 purchase totals =	$943.31		$1,030.8286	$1,030.82	$1,030.80	$1,030.70