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	$169.27	11.781%	$189.2117	$189.21	$189.20	$189.20
Purchase #2	$136.48	5.300%	$143.7134	$143.71	$143.70	$143.70
Purchase #3	$192.41	11.231%	$214.0196	$214.02	$214.00	$214.00
Purchase #4	$50.26	4.366%	$52.4544	$52.45	$52.45	$52.50
Purchase #5	$88.27	11.510%	$98.4299	$98.43	$98.45	$98.40
Purchase #6	$63.83	12.675%	$71.9205	$71.92	$71.90	$71.90
Purchase #7	$162.53	4.547%	$169.9202	$169.92	$169.90	$169.90
7 purchase totals =	$863.05		$939.6697	$939.66	$939.60	$939.60