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	$94.60	10.503%	$104.5358	$104.54	$104.55	$104.50
Purchase #2	$250.90	3.116%	$258.718	$258.72	$258.70	$258.70
Purchase #3	$31.94	10.225%	$35.2059	$35.21	$35.20	$35.20
Purchase #4	$133.36	4.509%	$139.3732	$139.37	$139.35	$139.40
Purchase #5	$33.56	3.685%	$34.7967	$34.80	$34.80	$34.80
Purchase #6	$80.87	11.163%	$89.8975	$89.90	$89.90	$89.90
Purchase #7	$110.55	8.417%	$119.855	$119.86	$119.85	$119.90
7 purchase totals =	$735.78		$782.3821	$782.40	$782.35	$782.40