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	$225.36	4.158%	$234.7305	$234.73	$234.75	$234.70
Purchase #2	$25.78	7.767%	$27.7823	$27.78	$27.80	$27.80
Purchase #3	$55.41	7.377%	$59.4976	$59.50	$59.50	$59.50
Purchase #4	$32.65	10.632%	$36.1213	$36.12	$36.10	$36.10
Purchase #5	$172.46	4.608%	$180.407	$180.41	$180.40	$180.40
Purchase #6	$70.43	11.440%	$78.4872	$78.49	$78.50	$78.50
Purchase #7	$26.28	6.280%	$27.9304	$27.93	$27.95	$27.90
7 purchase totals =	$608.37		$644.9563	$644.96	$645.00	$644.90