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	$29.72	13.440%	$33.7144	$33.71	$33.70	$33.70
Purchase #2	$131.66	8.857%	$143.3211	$143.32	$143.30	$143.30
Purchase #3	$174.94	6.740%	$186.731	$186.73	$186.75	$186.70
Purchase #4	$85.44	13.793%	$97.2247	$97.22	$97.20	$97.20
Purchase #5	$42.83	9.386%	$46.85	$46.85	$46.85	$46.90
Purchase #6	$219.52	13.842%	$249.906	$249.91	$249.90	$249.90
Purchase #7	$162.47	5.622%	$171.6041	$171.60	$171.60	$171.60
7 purchase totals =	$846.58		$929.3513	$929.34	$929.30	$929.30