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	$237.62	5.324%	$250.2709	$250.27	$250.25	$250.30
Purchase #2	$196.76	9.158%	$214.7793	$214.78	$214.80	$214.80
Purchase #3	$231.44	13.297%	$262.2146	$262.21	$262.20	$262.20
Purchase #4	$78.61	5.462%	$82.9037	$82.90	$82.90	$82.90
Purchase #5	$97.61	6.175%	$103.6374	$103.64	$103.65	$103.60
Purchase #6	$25.43	7.734%	$27.3968	$27.40	$27.40	$27.40
Purchase #7	$19.40	6.551%	$20.6709	$20.67	$20.65	$20.70
7 purchase totals =	$886.87		$961.8736	$961.87	$961.85	$961.90