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	$51.53	6.190%	$54.7197	$54.72	$54.70	$54.70
Purchase #2	$52.92	5.619%	$55.8936	$55.89	$55.90	$55.90
Purchase #3	$106.25	7.377%	$114.0881	$114.09	$114.10	$114.10
Purchase #4	$236.62	11.675%	$264.2454	$264.25	$264.25	$264.20
Purchase #5	$128.42	5.412%	$135.3701	$135.37	$135.35	$135.40
Purchase #6	$199.44	5.565%	$210.5388	$210.54	$210.55	$210.50
Purchase #7	$65.69	10.314%	$72.4653	$72.47	$72.45	$72.50
7 purchase totals =	$840.87		$907.3210	$907.33	$907.30	$907.30