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	$24.30	13.680%	$27.6242	$27.62	$27.60	$27.60
Purchase #2	$164.46	12.150%	$184.4419	$184.44	$184.45	$184.40
Purchase #3	$168.98	8.709%	$183.6965	$183.70	$183.70	$183.70
Purchase #4	$85.44	12.575%	$96.1841	$96.18	$96.20	$96.20
Purchase #5	$54.30	13.368%	$61.5588	$61.56	$61.55	$61.60
Purchase #6	$31.30	13.695%	$35.5865	$35.59	$35.60	$35.60
Purchase #7	$80.93	12.661%	$91.1765	$91.18	$91.20	$91.20
7 purchase totals =	$609.71		$680.2685	$680.27	$680.30	$680.30