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	$245.54	3.846%	$254.9835	$254.98	$255.00	$255.00
Purchase #2	$116.28	5.843%	$123.0742	$123.07	$123.05	$123.10
Purchase #3	$171.53	3.105%	$176.856	$176.86	$176.85	$176.90
Purchase #4	$167.29	8.111%	$180.8589	$180.86	$180.85	$180.90
Purchase #5	$99.93	13.498%	$113.4186	$113.42	$113.40	$113.40
Purchase #6	$204.80	8.355%	$221.911	$221.91	$221.90	$221.90
Purchase #7	$183.36	3.556%	$189.8803	$189.88	$189.90	$189.90
7 purchase totals =	$1,188.73		$1,260.9825	$1,260.98	$1,260.95	$1,261.10