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	$6.92	5.392%	$7.2931	$7.29	$7.30	$7.30
Purchase #2	$18.94	9.623%	$20.7626	$20.76	$20.75	$20.80
Purchase #3	$72.56	13.496%	$82.3527	$82.35	$82.35	$82.40
Purchase #4	$37.51	3.561%	$38.8457	$38.85	$38.85	$38.80
Purchase #5	$131.88	6.127%	$139.9603	$139.96	$139.95	$140.00
Purchase #6	$33.41	11.792%	$37.3497	$37.35	$37.35	$37.30
Purchase #7	$27.35	10.169%	$30.1312	$30.13	$30.15	$30.10
7 purchase totals =	$328.57		$356.6953	$356.69	$356.70	$356.70