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	$100.48	9.394%	$109.9191	$109.92	$109.90	$109.90
Purchase #2	$57.31	12.587%	$64.5236	$64.52	$64.50	$64.50
Purchase #3	$48.79	13.595%	$55.423	$55.42	$55.40	$55.40
Purchase #4	$211.80	13.845%	$241.1237	$241.12	$241.10	$241.10
Purchase #5	$224.90	3.299%	$232.3195	$232.32	$232.30	$232.30
Purchase #6	$233.39	4.611%	$244.1516	$244.15	$244.15	$244.20
Purchase #7	$131.67	9.352%	$143.9838	$143.98	$144.00	$144.00
7 purchase totals =	$1,008.34		$1,091.4443	$1,091.43	$1,091.35	$1,091.40