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	$6.86	12.600%	$7.7244	$7.72	$7.70	$7.70
Purchase #2	$16.35	11.759%	$18.2726	$18.27	$18.25	$18.30
Purchase #3	$165.70	13.565%	$188.1772	$188.18	$188.20	$188.20
Purchase #4	$56.50	10.646%	$62.515	$62.52	$62.50	$62.50
Purchase #5	$33.83	9.766%	$37.1338	$37.13	$37.15	$37.10
Purchase #6	$86.45	12.637%	$97.3747	$97.37	$97.35	$97.40
Purchase #7	$72.51	8.527%	$78.6929	$78.69	$78.70	$78.70
7 purchase totals =	$438.20		$489.8906	$489.88	$489.85	$489.90