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	$31.68	6.121%	$33.6191	$33.62	$33.60	$33.60
Purchase #2	$117.95	8.156%	$127.57	$127.57	$127.55	$127.60
Purchase #3	$247.62	3.741%	$256.8835	$256.88	$256.90	$256.90
Purchase #4	$198.68	6.340%	$211.2763	$211.28	$211.30	$211.30
Purchase #5	$128.60	6.227%	$136.6079	$136.61	$136.60	$136.60
Purchase #6	$85.86	4.440%	$89.6722	$89.67	$89.65	$89.70
Purchase #7	$167.60	11.128%	$186.2505	$186.25	$186.25	$186.30
7 purchase totals =	$977.99		$1,041.8795	$1,041.88	$1,041.85	$1,042.00