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	$85.30	5.413%	$89.9173	$89.92	$89.90	$89.90
Purchase #2	$84.50	5.342%	$89.014	$89.01	$89.00	$89.00
Purchase #3	$219.68	7.318%	$235.7562	$235.76	$235.75	$235.80
Purchase #4	$239.52	8.300%	$259.4002	$259.40	$259.40	$259.40
Purchase #5	$63.78	3.833%	$66.2247	$66.22	$66.20	$66.20
Purchase #6	$41.61	4.183%	$43.3505	$43.35	$43.35	$43.40
Purchase #7	$149.61	8.763%	$162.7203	$162.72	$162.70	$162.70
7 purchase totals =	$884.00		$946.3832	$946.38	$946.30	$946.40