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	$82.63	5.669%	$87.3143	$87.31	$87.30	$87.30
Purchase #2	$222.38	5.279%	$234.1194	$234.12	$234.10	$234.10
Purchase #3	$156.42	4.598%	$163.6122	$163.61	$163.60	$163.60
Purchase #4	$28.44	12.456%	$31.9825	$31.98	$32.00	$32.00
Purchase #5	$49.98	11.835%	$55.8951	$55.90	$55.90	$55.90
Purchase #6	$52.43	13.737%	$59.6323	$59.63	$59.65	$59.60
Purchase #7	$143.43	9.321%	$156.7991	$156.80	$156.80	$156.80
7 purchase totals =	$735.71		$789.3549	$789.35	$789.35	$789.30