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	$124.43	5.435%	$131.1928	$131.19	$131.20	$131.20
Purchase #2	$153.83	11.257%	$171.1466	$171.15	$171.15	$171.10
Purchase #3	$10.55	6.581%	$11.2443	$11.24	$11.25	$11.20
Purchase #4	$39.62	9.769%	$43.4905	$43.49	$43.50	$43.50
Purchase #5	$246.58	12.661%	$277.7995	$277.80	$277.80	$277.80
Purchase #6	$219.96	13.422%	$249.483	$249.48	$249.50	$249.50
Purchase #7	$57.89	12.756%	$65.2744	$65.27	$65.25	$65.30
7 purchase totals =	$852.86		$949.6311	$949.62	$949.65	$949.60