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	$41.89	13.215%	$47.4258	$47.43	$47.45	$47.40
Purchase #2	$198.50	10.410%	$219.1639	$219.16	$219.15	$219.20
Purchase #3	$25.78	12.175%	$28.9187	$28.92	$28.90	$28.90
Purchase #4	$36.63	11.250%	$40.7509	$40.75	$40.75	$40.80
Purchase #5	$143.75	6.296%	$152.8005	$152.80	$152.80	$152.80
Purchase #6	$19.59	7.590%	$21.0769	$21.08	$21.10	$21.10
Purchase #7	$242.33	10.816%	$268.5404	$268.54	$268.55	$268.50
7 purchase totals =	$708.47		$778.6771	$778.68	$778.70	$778.70