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	$96.93	3.580%	$100.4001	$100.40	$100.40	$100.40
Purchase #2	$81.75	9.838%	$89.7926	$89.79	$89.80	$89.80
Purchase #3	$86.90	12.488%	$97.7521	$97.75	$97.75	$97.80
Purchase #4	$83.36	11.365%	$92.8339	$92.83	$92.85	$92.80
Purchase #5	$165.59	8.545%	$179.7397	$179.74	$179.75	$179.70
Purchase #6	$172.80	13.575%	$196.2576	$196.26	$196.25	$196.30
Purchase #7	$125.48	6.223%	$133.2886	$133.29	$133.30	$133.30
7 purchase totals =	$812.81		$890.0646	$890.06	$890.10	$890.10