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	$25.52	5.863%	$27.0162	$27.02	$27.00	$27.00
Purchase #2	$245.83	11.800%	$274.8379	$274.84	$274.85	$274.80
Purchase #3	$150.78	7.744%	$162.4564	$162.46	$162.45	$162.50
Purchase #4	$131.49	12.331%	$147.704	$147.70	$147.70	$147.70
Purchase #5	$37.78	6.157%	$40.1061	$40.11	$40.10	$40.10
Purchase #6	$93.41	5.466%	$98.5158	$98.52	$98.50	$98.50
Purchase #7	$20.98	7.462%	$22.5455	$22.55	$22.55	$22.50
7 purchase totals =	$705.79		$773.1819	$773.20	$773.15	$773.10