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	$94.56	6.214%	$100.436	$100.44	$100.45	$100.40
Purchase #2	$199.76	10.323%	$220.3812	$220.38	$220.40	$220.40
Purchase #3	$11.32	5.452%	$11.9372	$11.94	$11.95	$11.90
Purchase #4	$80.50	8.663%	$87.4737	$87.47	$87.45	$87.50
Purchase #5	$188.96	11.213%	$210.1481	$210.15	$210.15	$210.10
Purchase #6	$114.30	8.564%	$124.0887	$124.09	$124.10	$124.10
Purchase #7	$58.78	11.713%	$65.6649	$65.66	$65.65	$65.70
7 purchase totals =	$748.18		$820.1298	$820.13	$820.15	$820.10