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	$59.79	9.301%	$65.3511	$65.35	$65.35	$65.40
Purchase #2	$111.35	12.559%	$125.3344	$125.33	$125.35	$125.30
Purchase #3	$241.77	13.272%	$273.8577	$273.86	$273.85	$273.90
Purchase #4	$86.32	3.697%	$89.5113	$89.51	$89.50	$89.50
Purchase #5	$238.39	12.158%	$267.3735	$267.37	$267.35	$267.40
Purchase #6	$97.91	12.242%	$109.8961	$109.90	$109.90	$109.90
Purchase #7	$144.32	11.139%	$160.3958	$160.40	$160.40	$160.40
7 purchase totals =	$979.85		$1,091.7199	$1,091.72	$1,091.70	$1,091.80