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	$208.54	11.479%	$232.4783	$232.48	$232.50	$232.50
Purchase #2	$8.45	6.275%	$8.9802	$8.98	$9.00	$9.00
Purchase #3	$150.74	12.709%	$169.8975	$169.90	$169.90	$169.90
Purchase #4	$150.27	5.739%	$158.894	$158.89	$158.90	$158.90
Purchase #5	$150.48	9.533%	$164.8253	$164.83	$164.85	$164.80
Purchase #6	$29.72	5.638%	$31.3956	$31.40	$31.40	$31.40
Purchase #7	$141.65	12.490%	$159.3421	$159.34	$159.35	$159.30
7 purchase totals =	$839.85		$925.8130	$925.82	$925.90	$925.80