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	$38.75	5.587%	$40.915	$40.92	$40.90	$40.90
Purchase #2	$226.89	7.296%	$243.4439	$243.44	$243.45	$243.40
Purchase #3	$75.34	13.449%	$85.4725	$85.47	$85.45	$85.50
Purchase #4	$98.99	10.444%	$109.3285	$109.33	$109.35	$109.30
Purchase #5	$204.26	13.466%	$231.7657	$231.77	$231.75	$231.80
Purchase #6	$181.57	10.514%	$200.6603	$200.66	$200.65	$200.70
Purchase #7	$89.80	9.296%	$98.1478	$98.15	$98.15	$98.10
7 purchase totals =	$915.60		$1,009.7337	$1,009.74	$1,009.70	$1,009.70