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	$91.59	12.253%	$102.8125	$102.81	$102.80	$102.80
Purchase #2	$38.59	11.170%	$42.9005	$42.90	$42.90	$42.90
Purchase #3	$92.29	5.365%	$97.2414	$97.24	$97.25	$97.20
Purchase #4	$188.81	8.181%	$204.2565	$204.26	$204.25	$204.30
Purchase #5	$87.48	5.531%	$92.3185	$92.32	$92.30	$92.30
Purchase #6	$147.48	13.766%	$167.7821	$167.78	$167.80	$167.80
Purchase #7	$244.30	12.231%	$274.1803	$274.18	$274.20	$274.20
7 purchase totals =	$890.54		$981.4918	$981.49	$981.50	$981.50