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	$83.76	6.302%	$89.0386	$89.04	$89.05	$89.00
Purchase #2	$72.35	5.296%	$76.1817	$76.18	$76.20	$76.20
Purchase #3	$248.51	12.155%	$278.7164	$278.72	$278.70	$278.70
Purchase #4	$93.40	13.177%	$105.7073	$105.71	$105.70	$105.70
Purchase #5	$194.26	12.742%	$219.0126	$219.01	$219.00	$219.00
Purchase #6	$56.75	12.520%	$63.8551	$63.86	$63.85	$63.90
Purchase #7	$247.31	8.391%	$268.0618	$268.06	$268.05	$268.10
7 purchase totals =	$996.34		$1,100.5735	$1,100.58	$1,100.55	$1,100.60