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	$217.83	11.516%	$242.9153	$242.92	$242.90	$242.90
Purchase #2	$79.83	3.837%	$82.8931	$82.89	$82.90	$82.90
Purchase #3	$38.69	13.527%	$43.9236	$43.92	$43.90	$43.90
Purchase #4	$40.87	6.583%	$43.5605	$43.56	$43.55	$43.60
Purchase #5	$6.90	6.331%	$7.3368	$7.34	$7.35	$7.30
Purchase #6	$170.50	11.761%	$190.5525	$190.55	$190.55	$190.60
Purchase #7	$237.30	12.550%	$267.0812	$267.08	$267.10	$267.10
7 purchase totals =	$791.92		$878.2630	$878.26	$878.25	$878.30