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	$38.31	9.165%	$41.8211	$41.82	$41.80	$41.80
Purchase #2	$100.31	13.703%	$114.0555	$114.06	$114.05	$114.10
Purchase #3	$19.92	6.430%	$21.2009	$21.20	$21.20	$21.20
Purchase #4	$35.34	8.354%	$38.2923	$38.29	$38.30	$38.30
Purchase #5	$32.65	8.624%	$35.4657	$35.47	$35.45	$35.50
Purchase #6	$59.32	5.869%	$62.8015	$62.80	$62.80	$62.80
Purchase #7	$72.99	12.417%	$82.0532	$82.05	$82.05	$82.10
7 purchase totals =	$358.84		$395.6902	$395.69	$395.65	$395.80