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	$28.79	8.772%	$31.3155	$31.32	$31.30	$31.30
Purchase #2	$137.64	4.133%	$143.3287	$143.33	$143.35	$143.30
Purchase #3	$85.99	7.165%	$92.1512	$92.15	$92.15	$92.20
Purchase #4	$90.38	11.189%	$100.4926	$100.49	$100.50	$100.50
Purchase #5	$113.46	8.730%	$123.3651	$123.37	$123.35	$123.40
Purchase #6	$109.35	12.155%	$122.6415	$122.64	$122.65	$122.60
Purchase #7	$218.42	13.259%	$247.3803	$247.38	$247.40	$247.40
7 purchase totals =	$784.03		$860.6749	$860.68	$860.70	$860.70