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	$62.48	12.278%	$70.1513	$70.15	$70.15	$70.20
Purchase #2	$88.34	10.663%	$97.7597	$97.76	$97.75	$97.80
Purchase #3	$178.89	10.261%	$197.2459	$197.25	$197.25	$197.20
Purchase #4	$208.90	11.807%	$233.5648	$233.56	$233.55	$233.60
Purchase #5	$79.43	13.416%	$90.0863	$90.09	$90.10	$90.10
Purchase #6	$72.69	10.752%	$80.5056	$80.51	$80.50	$80.50
Purchase #7	$90.42	10.127%	$99.5768	$99.58	$99.60	$99.60
7 purchase totals =	$781.15		$868.8904	$868.90	$868.90	$869.00