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	$29.68	10.518%	$32.8017	$32.80	$32.80	$32.80
Purchase #2	$116.82	11.701%	$130.4891	$130.49	$130.50	$130.50
Purchase #3	$219.87	3.434%	$227.4203	$227.42	$227.40	$227.40
Purchase #4	$220.32	13.722%	$250.5523	$250.55	$250.55	$250.60
Purchase #5	$102.90	6.778%	$109.8746	$109.87	$109.85	$109.90
Purchase #6	$129.93	7.159%	$139.2317	$139.23	$139.25	$139.20
Purchase #7	$202.82	13.173%	$229.5375	$229.54	$229.55	$229.50
7 purchase totals =	$1,022.34		$1,119.9072	$1,119.90	$1,119.90	$1,119.90