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	$24.41	13.803%	$27.7793	$27.78	$27.80	$27.80
Purchase #2	$145.37	7.355%	$156.062	$156.06	$156.05	$156.10
Purchase #3	$112.42	10.605%	$124.3421	$124.34	$124.35	$124.30
Purchase #4	$227.50	3.194%	$234.7664	$234.77	$234.75	$234.80
Purchase #5	$193.28	3.699%	$200.4294	$200.43	$200.45	$200.40
Purchase #6	$71.33	10.159%	$78.5764	$78.58	$78.60	$78.60
Purchase #7	$187.29	12.505%	$210.7106	$210.71	$210.70	$210.70
7 purchase totals =	$961.60		$1,032.6662	$1,032.67	$1,032.70	$1,032.70