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	$132.70	7.213%	$142.2717	$142.27	$142.25	$142.30
Purchase #2	$215.98	12.203%	$242.336	$242.34	$242.35	$242.30
Purchase #3	$143.66	9.610%	$157.4657	$157.47	$157.45	$157.50
Purchase #4	$85.87	4.356%	$89.6105	$89.61	$89.60	$89.60
Purchase #5	$85.72	4.825%	$89.856	$89.86	$89.85	$89.90
Purchase #6	$76.62	8.120%	$82.8415	$82.84	$82.85	$82.80
Purchase #7	$31.77	4.705%	$33.2648	$33.26	$33.25	$33.30
7 purchase totals =	$772.32		$837.6462	$837.65	$837.60	$837.70