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	$36.55	13.238%	$41.3885	$41.39	$41.40	$41.40
Purchase #2	$150.36	11.848%	$168.1747	$168.17	$168.15	$168.20
Purchase #3	$172.48	7.836%	$185.9955	$186.00	$186.00	$186.00
Purchase #4	$165.36	7.123%	$177.1386	$177.14	$177.15	$177.10
Purchase #5	$74.59	11.349%	$83.0552	$83.06	$83.05	$83.10
Purchase #6	$41.66	5.463%	$43.9359	$43.94	$43.95	$43.90
Purchase #7	$57.87	13.736%	$65.819	$65.82	$65.80	$65.80
7 purchase totals =	$698.87		$765.5074	$765.52	$765.50	$765.50