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	$68.56	11.809%	$76.6563	$76.66	$76.65	$76.70
Purchase #2	$176.73	5.119%	$185.7768	$185.78	$185.80	$185.80
Purchase #3	$172.85	10.645%	$191.2499	$191.25	$191.25	$191.20
Purchase #4	$39.67	10.159%	$43.7001	$43.70	$43.70	$43.70
Purchase #5	$103.32	3.150%	$106.5746	$106.57	$106.55	$106.60
Purchase #6	$65.66	13.385%	$74.4486	$74.45	$74.45	$74.40
Purchase #7	$89.31	9.741%	$98.0097	$98.01	$98.00	$98.00
7 purchase totals =	$716.10		$776.4160	$776.42	$776.40	$776.40