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	$155.61	5.128%	$163.5897	$163.59	$163.60	$163.60
Purchase #2	$98.30	10.804%	$108.9203	$108.92	$108.90	$108.90
Purchase #3	$73.33	12.411%	$82.431	$82.43	$82.45	$82.40
Purchase #4	$94.81	5.171%	$99.7126	$99.71	$99.70	$99.70
Purchase #5	$109.75	9.219%	$119.8679	$119.87	$119.85	$119.90
Purchase #6	$94.93	7.736%	$102.2738	$102.27	$102.25	$102.30
Purchase #7	$218.28	7.145%	$233.8761	$233.88	$233.90	$233.90
7 purchase totals =	$845.01		$910.6714	$910.67	$910.65	$910.70