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	$69.53	3.682%	$72.0901	$72.09	$72.10	$72.10
Purchase #2	$242.68	11.269%	$270.0276	$270.03	$270.05	$270.00
Purchase #3	$52.89	8.837%	$57.5639	$57.56	$57.55	$57.60
Purchase #4	$134.81	4.382%	$140.7174	$140.72	$140.70	$140.70
Purchase #5	$68.46	11.850%	$76.5725	$76.57	$76.55	$76.60
Purchase #6	$180.92	8.845%	$196.9224	$196.92	$196.90	$196.90
Purchase #7	$95.28	3.279%	$98.4042	$98.40	$98.40	$98.40
7 purchase totals =	$844.57		$912.2981	$912.29	$912.25	$912.30