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	$230.28	8.566%	$250.0058	$250.01	$250.00	$250.00
Purchase #2	$38.95	6.579%	$41.5125	$41.51	$41.50	$41.50
Purchase #3	$228.67	6.412%	$243.3323	$243.33	$243.35	$243.30
Purchase #4	$78.69	13.201%	$89.0779	$89.08	$89.10	$89.10
Purchase #5	$109.41	9.557%	$119.8663	$119.87	$119.85	$119.90
Purchase #6	$48.43	9.568%	$53.0638	$53.06	$53.05	$53.10
Purchase #7	$184.90	7.663%	$199.0689	$199.07	$199.05	$199.10
7 purchase totals =	$919.33		$995.9275	$995.93	$995.90	$996.00