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	$103.82	12.260%	$116.5483	$116.55	$116.55	$116.50
Purchase #2	$242.51	11.346%	$270.0252	$270.03	$270.05	$270.00
Purchase #3	$91.88	12.579%	$103.4376	$103.44	$103.45	$103.40
Purchase #4	$130.60	6.434%	$139.0028	$139.00	$139.00	$139.00
Purchase #5	$50.31	10.258%	$55.4708	$55.47	$55.45	$55.50
Purchase #6	$250.84	6.375%	$266.8311	$266.83	$266.85	$266.80
Purchase #7	$33.49	6.334%	$35.6113	$35.61	$35.60	$35.60
7 purchase totals =	$903.45		$986.9271	$986.93	$986.95	$986.80