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	$33.97	11.526%	$37.8854	$37.89	$37.90	$37.90
Purchase #2	$45.77	4.472%	$47.8168	$47.82	$47.80	$47.80
Purchase #3	$186.76	12.175%	$209.498	$209.50	$209.50	$209.50
Purchase #4	$41.79	11.329%	$46.5244	$46.52	$46.50	$46.50
Purchase #5	$233.67	12.653%	$263.2363	$263.24	$263.25	$263.20
Purchase #6	$240.86	6.833%	$257.318	$257.32	$257.30	$257.30
Purchase #7	$134.33	7.797%	$144.8037	$144.80	$144.80	$144.80
7 purchase totals =	$917.15		$1,007.0826	$1,007.09	$1,007.05	$1,007.00