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	$29.27	12.862%	$33.0347	$33.03	$33.05	$33.00
Purchase #2	$212.50	12.182%	$238.3868	$238.39	$238.40	$238.40
Purchase #3	$123.61	6.640%	$131.8177	$131.82	$131.80	$131.80
Purchase #4	$43.88	10.361%	$48.4264	$48.43	$48.45	$48.40
Purchase #5	$170.92	6.431%	$181.9119	$181.91	$181.90	$181.90
Purchase #6	$79.73	9.566%	$87.357	$87.36	$87.35	$87.40
Purchase #7	$37.78	7.247%	$40.5179	$40.52	$40.50	$40.50
7 purchase totals =	$697.69		$761.4524	$761.46	$761.45	$761.40