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	$76.34	3.128%	$78.7279	$78.73	$78.75	$78.70
Purchase #2	$99.39	10.105%	$109.4334	$109.43	$109.45	$109.40
Purchase #3	$209.56	10.802%	$232.1967	$232.20	$232.20	$232.20
Purchase #4	$111.56	6.223%	$118.5024	$118.50	$118.50	$118.50
Purchase #5	$202.34	7.413%	$217.3395	$217.34	$217.35	$217.30
Purchase #6	$189.79	4.665%	$198.6437	$198.64	$198.65	$198.60
Purchase #7	$155.34	10.593%	$171.7952	$171.80	$171.80	$171.80
7 purchase totals =	$1,044.32		$1,126.6388	$1,126.64	$1,126.70	$1,126.50