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	$142.47	5.667%	$150.5438	$150.54	$150.55	$150.50
Purchase #2	$207.84	3.628%	$215.3804	$215.38	$215.40	$215.40
Purchase #3	$42.26	9.514%	$46.2806	$46.28	$46.30	$46.30
Purchase #4	$202.57	7.542%	$217.8478	$217.85	$217.85	$217.80
Purchase #5	$79.49	9.311%	$86.8913	$86.89	$86.90	$86.90
Purchase #6	$161.85	7.851%	$174.5568	$174.56	$174.55	$174.60
Purchase #7	$148.37	6.375%	$157.8286	$157.83	$157.85	$157.80
7 purchase totals =	$984.85		$1,049.3293	$1,049.33	$1,049.40	$1,049.30