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	$117.26	5.252%	$123.4185	$123.42	$123.40	$123.40
Purchase #2	$234.54	4.659%	$245.4672	$245.47	$245.45	$245.50
Purchase #3	$24.36	7.363%	$26.1536	$26.15	$26.15	$26.20
Purchase #4	$120.29	6.870%	$128.5539	$128.55	$128.55	$128.60
Purchase #5	$243.89	4.560%	$255.0114	$255.01	$255.00	$255.00
Purchase #6	$94.76	4.811%	$99.3189	$99.32	$99.30	$99.30
Purchase #7	$220.28	11.826%	$246.3303	$246.33	$246.35	$246.30
7 purchase totals =	$1,055.38		$1,124.2538	$1,124.25	$1,124.20	$1,124.30