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	$55.65	3.377%	$57.5293	$57.53	$57.55	$57.50
Purchase #2	$94.82	11.259%	$105.4958	$105.50	$105.50	$105.50
Purchase #3	$41.65	13.128%	$47.1178	$47.12	$47.10	$47.10
Purchase #4	$206.48	13.294%	$233.9295	$233.93	$233.95	$233.90
Purchase #5	$82.59	10.602%	$91.3462	$91.35	$91.35	$91.30
Purchase #6	$202.27	12.661%	$227.8794	$227.88	$227.90	$227.90
Purchase #7	$83.82	7.191%	$89.8475	$89.85	$89.85	$89.80
7 purchase totals =	$767.28		$853.1455	$853.16	$853.20	$853.00