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	$20.85	11.736%	$23.297	$23.30	$23.30	$23.30
Purchase #2	$202.86	6.561%	$216.1696	$216.17	$216.15	$216.20
Purchase #3	$158.78	12.298%	$178.3068	$178.31	$178.30	$178.30
Purchase #4	$127.76	10.352%	$140.9857	$140.99	$141.00	$141.00
Purchase #5	$218.32	3.204%	$225.315	$225.32	$225.30	$225.30
Purchase #6	$55.25	7.713%	$59.5114	$59.51	$59.50	$59.50
Purchase #7	$168.51	9.389%	$184.3314	$184.33	$184.35	$184.30
7 purchase totals =	$952.33		$1,027.9169	$1,027.93	$1,027.90	$1,027.90