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	$233.40	10.664%	$258.2898	$258.29	$258.30	$258.30
Purchase #2	$109.59	12.717%	$123.5266	$123.53	$123.55	$123.50
Purchase #3	$241.57	6.590%	$257.4895	$257.49	$257.50	$257.50
Purchase #4	$92.31	5.165%	$97.0778	$97.08	$97.10	$97.10
Purchase #5	$82.99	7.518%	$89.2292	$89.23	$89.25	$89.20
Purchase #6	$144.79	10.727%	$160.3216	$160.32	$160.30	$160.30
Purchase #7	$37.92	13.437%	$43.0153	$43.02	$43.00	$43.00
7 purchase totals =	$942.57		$1,028.9498	$1,028.96	$1,029.00	$1,028.90