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	$243.31	5.743%	$257.2833	$257.28	$257.30	$257.30
Purchase #2	$78.48	6.588%	$83.6503	$83.65	$83.65	$83.70
Purchase #3	$117.64	12.486%	$132.3285	$132.33	$132.35	$132.30
Purchase #4	$104.59	4.165%	$108.9462	$108.95	$108.95	$108.90
Purchase #5	$75.41	10.405%	$83.2564	$83.26	$83.25	$83.30
Purchase #6	$94.35	10.169%	$103.9445	$103.94	$103.95	$103.90
Purchase #7	$213.52	4.215%	$222.5199	$222.52	$222.50	$222.50
7 purchase totals =	$927.30		$991.9291	$991.93	$991.95	$991.90