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	$69.26	13.156%	$78.3718	$78.37	$78.35	$78.40
Purchase #2	$75.48	6.707%	$80.5424	$80.54	$80.55	$80.50
Purchase #3	$97.61	7.795%	$105.2187	$105.22	$105.20	$105.20
Purchase #4	$66.40	8.465%	$72.0208	$72.02	$72.00	$72.00
Purchase #5	$63.89	4.740%	$66.9184	$66.92	$66.90	$66.90
Purchase #6	$232.25	11.678%	$259.3722	$259.37	$259.35	$259.40
Purchase #7	$43.98	8.738%	$47.823	$47.82	$47.80	$47.80
7 purchase totals =	$648.87		$710.2673	$710.26	$710.15	$710.20