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	$78.93	4.470%	$82.4582	$82.46	$82.45	$82.50
Purchase #2	$79.79	8.296%	$86.4094	$86.41	$86.40	$86.40
Purchase #3	$100.71	5.265%	$106.0124	$106.01	$106.00	$106.00
Purchase #4	$204.29	4.284%	$213.0418	$213.04	$213.05	$213.00
Purchase #5	$237.31	13.457%	$269.2448	$269.24	$269.25	$269.20
Purchase #6	$169.39	13.212%	$191.7698	$191.77	$191.75	$191.80
Purchase #7	$36.65	12.231%	$41.1327	$41.13	$41.15	$41.10
7 purchase totals =	$907.07		$990.0691	$990.06	$990.05	$990.00