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	$122.73	7.393%	$131.8034	$131.80	$131.80	$131.80
Purchase #2	$100.51	13.790%	$114.3703	$114.37	$114.35	$114.40
Purchase #3	$128.39	12.460%	$144.3874	$144.39	$144.40	$144.40
Purchase #4	$228.69	13.725%	$260.0777	$260.08	$260.10	$260.10
Purchase #5	$83.43	6.851%	$89.1458	$89.15	$89.15	$89.10
Purchase #6	$228.73	6.442%	$243.4648	$243.46	$243.45	$243.50
Purchase #7	$238.39	10.570%	$263.5878	$263.59	$263.60	$263.60
7 purchase totals =	$1,130.87		$1,246.8372	$1,246.84	$1,246.85	$1,246.90